content/config/pmd/category/java/errorprone.xml

<?xml version="1.0"?>

<ruleset name="Error Prone"
         xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.sourceforge.io/ruleset_2_0_0.xsd">

    <description>
        Rules to detect constructs that are either broken, extremely confusing or prone to runtime errors.
    </description>

    <rule name="AssignmentInOperand"
          since="1.03"
          message="Avoid assignments in operands"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AssignmentInOperandRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#assignmentinoperand">
        <description>
            Avoid assignments in operands; this can make code more complicated and harder to read.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public void bar() {
    int x = 2;
    if ((x = getX()) == 3) {
      System.out.println("3!");
    }
}
]]>
        </example>
    </rule>

    <rule name="AssignmentToNonFinalStatic"
          since="2.2"
          message="Possible unsafe assignment to a non-final static field in a constructor."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AssignmentToNonFinalStaticRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#assignmenttononfinalstatic">
        <description>
            Identifies a possible unsafe usage of a static field.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class StaticField {
   static int x;
   public FinalFields(int y) {
    x = y; // unsafe
   }
}
]]>
        </example>
    </rule>

    <rule name="AvoidAccessibilityAlteration"
          language="java"
          since="4.1"
          message="You should not modify visibility of class or methods using getDeclaredConstructors(), getDeclaredConstructor(Class[]), setAccessible() or PrivilegedAction."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidaccessibilityalteration">
        <description>
            Methods such as getDeclaredConstructors(), getDeclaredConstructor(Class[]) and setAccessible(),
            as the interface PrivilegedAction, allow for the runtime alteration of variable, class, or
            method visibility, even if they are private. This violates the principle of encapsulation.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//PrimaryExpression[
(
(PrimarySuffix[
        ends-with(@Image,'getDeclaredConstructors')
                or
        ends-with(@Image,'getDeclaredConstructor')
                or
        ends-with(@Image,'setAccessible')
        ])
or
(PrimaryPrefix/Name[
        ends-with(@Image,'getDeclaredConstructor')
        or
        ends-with(@Image,'getDeclaredConstructors')
        or
        starts-with(@Image,'AccessibleObject.setAccessible')
        ])
)
and
(//ImportDeclaration/Name[
        contains(@Image,'java.security.PrivilegedAction')])
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Method;
import java.security.PrivilegedAction;

public class Violation {
  public void invalidCallsInMethod() throws SecurityException, NoSuchMethodException {
    // Possible call to forbidden getDeclaredConstructors
    Class[] arrayOfClass = new Class[1];
    this.getClass().getDeclaredConstructors();
    this.getClass().getDeclaredConstructor(arrayOfClass);
    Class clazz = this.getClass();
    clazz.getDeclaredConstructor(arrayOfClass);
    clazz.getDeclaredConstructors();
      // Possible call to forbidden setAccessible
    clazz.getMethod("", arrayOfClass).setAccessible(false);
    AccessibleObject.setAccessible(null, false);
    Method.setAccessible(null, false);
    Method[] methodsArray = clazz.getMethods();
    int nbMethod;
    for ( nbMethod = 0; nbMethod < methodsArray.length; nbMethod++ ) {
      methodsArray[nbMethod].setAccessible(false);
    }

      // Possible call to forbidden PrivilegedAction
    PrivilegedAction priv = (PrivilegedAction) new Object(); priv.run();
  }
}
]]>
        </example>
    </rule>

    <rule name="AvoidAssertAsIdentifier"
          language="java"
          since="3.4"
          message="Avoid using assert as an identifier; it became a reserved word in JDK 1.4"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidassertasidentifier">
        <description>
            Use of the term 'assert' will conflict with newer versions of Java since it is a reserved word.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>//VariableDeclaratorId[@Image='assert']</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class A {
    public class Foo {
        String assert = "foo";
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidBranchingStatementAsLastInLoop"
          since="5.0"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidBranchingStatementAsLastInLoopRule"
          message="Avoid using a branching statement as the last in a loop."
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidbranchingstatementaslastinloop">
        <description>
            Using a branching statement as the last part of a loop may be a bug, and/or is confusing.
            Ensure that the usage is not a bug, or consider using another approach.
        </description>
        <priority>2</priority>
        <example>
            <![CDATA[
// unusual use of branching statement in a loop
for (int i = 0; i < 10; i++) {
    if (i*i <= 25) {
        continue;
    }
    break;
}

// this makes more sense...
for (int i = 0; i < 10; i++) {
    if (i*i > 25) {
        break;
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidCallingFinalize"
          since="3.0"
          message="Avoid calling finalize() explicitly"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidCallingFinalizeRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidcallingfinalize">
        <description>
            The method Object.finalize() is called by the garbage collector on an object when garbage collection determines
            that there are no more references to the object. It should not be invoked by application logic.

            Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
void foo() {
    Bar b = new Bar();
    b.finalize();
}
]]>
        </example>
    </rule>

    <rule name="AvoidCatchingNPE"
          language="java"
          since="1.8"
          message="Avoid catching NullPointerException; consider removing the cause of the NPE."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidcatchingnpe">
        <description>
            Code should never throw NullPointerExceptions under normal circumstances.  A catch block may hide the
            original error, causing other, more subtle problems later on.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//CatchStatement/FormalParameter/Type
 /ReferenceType/ClassOrInterfaceType[@Image='NullPointerException']
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    void bar() {
        try {
            // do something
        } catch (NullPointerException npe) {
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidCatchingThrowable"
          since="1.2"
          message="A catch statement should never catch throwable since it includes errors."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidCatchingThrowableRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidcatchingthrowable">
        <description>
            Catching Throwable errors is not recommended since its scope is very broad. It includes runtime issues such as
            OutOfMemoryError that should be exposed and managed separately.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public void bar() {
    try {
        // do something
    } catch (Throwable th) {  // should not catch Throwable
        th.printStackTrace();
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidDecimalLiteralsInBigDecimalConstructor"
          language="java"
          since="3.4"
          message="Avoid creating BigDecimal with a decimal (float/double) literal. Use a String literal"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoiddecimalliteralsinbigdecimalconstructor">
        <description>
            One might assume that the result of "new BigDecimal(0.1)" is exactly equal to 0.1, but it is actually
            equal to .1000000000000000055511151231257827021181583404541015625.
            This is because 0.1 cannot be represented exactly as a double (or as a binary fraction of any finite
            length). Thus, the long value that is being passed in to the constructor is not exactly equal to 0.1,
            appearances notwithstanding.

            The (String) constructor, on the other hand, is perfectly predictable: 'new BigDecimal("0.1")' is
            exactly equal to 0.1, as one would expect.  Therefore, it is generally recommended that the
            (String) constructor be used in preference to this one.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//AllocationExpression
[ClassOrInterfaceType[@Image="BigDecimal"]]
[Arguments/ArgumentList/Expression/PrimaryExpression/PrimaryPrefix
    [
        Literal[(not(ends-with(@Image,'"'))) and contains(@Image,".")]
        or
        Name[ancestor::Block/BlockStatement/LocalVariableDeclaration
                [Type[PrimitiveType[@Image='double' or @Image='float']
                      or ReferenceType/ClassOrInterfaceType[@Image='Double' or @Image='Float']]]
                /VariableDeclarator/VariableDeclaratorId/@Image = @Image
            ]
        or
        Name[ancestor::MethodDeclaration/MethodDeclarator/FormalParameters/FormalParameter
                [Type[PrimitiveType[@Image='double' or @Image='float']
                      or ReferenceType/ClassOrInterfaceType[@Image='Double' or @Image='Float']]]
                /VariableDeclaratorId/@Image = @Image
            ]
    ]
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
BigDecimal bd = new BigDecimal(1.123);       // loss of precision, this would trigger the rule

BigDecimal bd = new BigDecimal("1.123");     // preferred approach

BigDecimal bd = new BigDecimal(12);          // preferred approach, ok for integer values
]]>
        </example>
    </rule>

    <rule name="AvoidDuplicateLiterals"
          since="1.0"
          message="The String literal {0} appears {1} times in this file; the first occurrence is on line {2}"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidDuplicateLiteralsRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidduplicateliterals">
        <description>
            Code containing duplicate String literals can usually be improved by declaring the String as a constant field.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
private void bar() {
     buz("Howdy");
     buz("Howdy");
     buz("Howdy");
     buz("Howdy");
}
private void buz(String x) {}
]]>
        </example>
    </rule>

    <rule name="AvoidEnumAsIdentifier"
          language="java"
          since="3.4"
          message="Avoid using enum as an identifier; it's a reserved word in JDK 1.5"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidenumasidentifier">
        <description>
            Use of the term 'enum' will conflict with newer versions of Java since it is a reserved word.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>//VariableDeclaratorId[@Image='enum']</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class A {
    public class Foo {
        String enum = "foo";
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidFieldNameMatchingMethodName"
          since="3.0"
          message="Field {0} has the same name as a method"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidFieldNameMatchingMethodNameRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidfieldnamematchingmethodname">
        <description>
            It can be confusing to have a field name with the same name as a method. While this is permitted,
            having information (field) and actions (method) is not clear naming. Developers versed in
            Smalltalk often prefer this approach as the methods denote accessor methods.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class Foo {
    Object bar;
    // bar is data or an action or both?
    void bar() {
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidFieldNameMatchingTypeName"
          since="3.0"
          message="It is somewhat confusing to have a field name matching the declaring class name"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidFieldNameMatchingTypeNameRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidfieldnamematchingtypename">
        <description>
            It is somewhat confusing to have a field name matching the declaring class name.
            This probably means that type and/or field names should be chosen more carefully.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class Foo extends Bar {
    int foo;    // There is probably a better name that can be used
}
]]>
        </example>
    </rule>

    <rule name="AvoidInstanceofChecksInCatchClause"
          language="java"
          since="3.0"
          message="An instanceof check is being performed on the caught exception.  Create a separate catch clause for this exception type."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidinstanceofchecksincatchclause">
        <description>
            Each caught exception type should be handled in its own catch clause.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//CatchStatement/FormalParameter
 /following-sibling::Block//InstanceOfExpression/PrimaryExpression/PrimaryPrefix
  /Name[
   @Image = ./ancestor::Block/preceding-sibling::FormalParameter
    /VariableDeclaratorId/@Image
  ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
try { // Avoid this
    // do something
} catch (Exception ee) {
    if (ee instanceof IOException) {
        cleanup();
    }
}

try {  // Prefer this:
    // do something
} catch (IOException ee) {
    cleanup();
}
]]>
        </example>
    </rule>

    <rule name="AvoidLiteralsInIfCondition"
          language="java"
          since="4.2.6"
          message="Avoid using Literals in Conditional Statements"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidliteralsinifcondition">
        <description>
            Avoid using hard-coded literals in conditional statements. By declaring them as static variables
            or private members with descriptive names maintainability is enhanced. By default, the literals "-1" and "0" are ignored.
            More exceptions can be defined with the property "ignoreMagicNumbers".
        </description>
        <priority>3</priority>
        <properties>
            <property name="ignoreMagicNumbers"
                      description="Comma-separated list of magic numbers, that should be ignored"
                      type="String" value="-1,0"/>
            <property name="xpath">
                <value>
                    <![CDATA[
//IfStatement/Expression/*/PrimaryExpression/PrimaryPrefix/Literal
[not(NullLiteral)]
[not(BooleanLiteral)]
[empty(index-of(tokenize($ignoreMagicNumbers, '\s*,\s*'), @Image))]
]]>
                </value>
            </property>
            <property name="version" value="2.0"/>
        </properties>
        <example>
            <![CDATA[
private static final int MAX_NUMBER_OF_REQUESTS = 10;

public void checkRequests() {

    if (i == 10) {                        // magic number, buried in a method
      doSomething();
    }

    if (i == MAX_NUMBER_OF_REQUESTS) {    // preferred approach
      doSomething();
    }

    if (aString.indexOf('.') != -1) {}     // magic number -1, by default ignored
    if (aString.indexOf('.') >= 0) { }     // alternative approach

    if (aDouble > 0.0) {}                  // magic number 0.0
    if (aDouble >= Double.MIN_VALUE) {}    // preferred approach
}
]]>
        </example>
    </rule>

    <rule name="AvoidLosingExceptionInformation"
          since="4.2.6"
          language="java"
          message="Avoid statements in a catch block that invoke accessors on the exception without using the information"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidlosingexceptioninformation">
        <description>
            Statements in a catch block that invoke accessors on the exception without using the information
            only add to code size.  Either remove the invocation, or use the return result.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//CatchStatement/Block/BlockStatement/Statement/StatementExpression/PrimaryExpression/PrimaryPrefix/Name
[
   @Image = concat(../../../../../../../FormalParameter/VariableDeclaratorId/@Image, '.getMessage')
   or
   @Image = concat(../../../../../../../FormalParameter/VariableDeclaratorId/@Image, '.getLocalizedMessage')
   or
   @Image = concat(../../../../../../../FormalParameter/VariableDeclaratorId/@Image, '.getCause')
   or
   @Image = concat(../../../../../../../FormalParameter/VariableDeclaratorId/@Image, '.getStackTrace')
   or
   @Image = concat(../../../../../../../FormalParameter/VariableDeclaratorId/@Image, '.toString')
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public void bar() {
    try {
        // do something
    } catch (SomeException se) {
        se.getMessage();
    }
}
]]>
        </example>
    </rule>

    <rule name="AvoidMultipleUnaryOperators"
          since="4.2"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidMultipleUnaryOperatorsRule"
          message="Using multiple unary operators may be a bug, and/or is confusing."
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidmultipleunaryoperators">
        <description>
            The use of multiple unary operators may be problematic, and/or confusing.
            Ensure that the intended usage is not a bug, or consider simplifying the expression.
        </description>
        <priority>2</priority>
        <example>
            <![CDATA[
// These are typo bugs, or at best needlessly complex and confusing:
int i = - -1;
int j = + - +1;
int z = ~~2;
boolean b = !!true;
boolean c = !!!true;

// These are better:
int i = 1;
int j = -1;
int z = 2;
boolean b = true;
boolean c = false;

// And these just make your brain hurt:
int i = ~-2;
int j = -~7;
]]>
        </example>
    </rule>

    <rule name="AvoidUsingOctalValues"
          since="3.9"
          message="Do not start a literal by 0 unless it's an octal value"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.AvoidUsingOctalValuesRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#avoidusingoctalvalues">
        <description>
            Integer literals should not start with zero since this denotes that the rest of literal will be
            interpreted as an octal value.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
int i = 012;    // set i with 10 not 12
int j = 010;    // set j with 8 not 10
k = i * j;      // set k with 80 not 120
]]>
        </example>
    </rule>

    <rule name="BadComparison"
          language="java"
          since="1.8"
          message="Avoid equality comparisons with Double.NaN"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#badcomparison">
        <description>
            Avoid equality comparisons with Double.NaN. Due to the implicit lack of representation
            precision when comparing floating point numbers these are likely to cause logic errors.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//EqualityExpression[@Image='==']
 /PrimaryExpression/PrimaryPrefix
 /Name[@Image='Double.NaN' or @Image='Float.NaN']
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
boolean x = (y == Double.NaN);
]]>
        </example>
    </rule>

    <rule name="BeanMembersShouldSerialize"
          since="1.1"
          message="Found non-transient, non-static member. Please mark as transient or provide accessors."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.BeanMembersShouldSerializeRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#beanmembersshouldserialize">
        <description>
            If a class is a bean, or is referenced by a bean directly or indirectly it needs to be serializable.
            Member variables need to be marked as transient, static, or have accessor methods in the class. Marking
            variables as transient is the safest and easiest modification. Accessor methods should follow the Java
            naming conventions, i.e. for a variable named foo, getFoo() and setFoo() accessor methods should be provided.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
private transient int someFoo;  // good, it's transient
private static int otherFoo;    // also OK
private int moreFoo;            // OK, has proper accessors, see below
private int badFoo;             // bad, should be marked transient

private void setMoreFoo(int moreFoo){
      this.moreFoo = moreFoo;
}

private int getMoreFoo(){
      return this.moreFoo;
}
]]>
        </example>
    </rule>

    <rule name="BrokenNullCheck"
          since="3.8"
          message="Method call on object which may be null"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.BrokenNullCheckRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#brokennullcheck">
        <description>
            The null check is broken since it will throw a NullPointerException itself.
            It is likely that you used || instead of &amp;&amp; or vice versa.
        </description>
        <priority>2</priority>
        <example>
            <![CDATA[
public String bar(String string) {
  // should be &&
    if (string!=null || !string.equals(""))
        return string;
  // should be ||
    if (string==null && string.equals(""))
        return string;
}
]]>
        </example>
    </rule>

    <rule name="CallSuperFirst"
          since="4.2.5"
          language="java"
          message="super should be called at the start of the method"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#callsuperfirst">
        <description>Super should be called at the start of the method</description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration[MethodDeclarator[
  @Image='onCreate' or
  @Image='onConfigurationChanged' or
  @Image='onPostCreate' or
  @Image='onPostResume' or
  @Image='onRestart' or
  @Image='onRestoreInstanceState' or
  @Image='onResume' or
  @Image='onStart'
  ]]
    /Block[not(
      (BlockStatement[1]/Statement/StatementExpression/PrimaryExpression[./PrimaryPrefix[@SuperModifier='true']]/PrimarySuffix[@Image= ancestor::MethodDeclaration/MethodDeclarator/@Image]))]
[ancestor::ClassOrInterfaceDeclaration[ExtendsList/ClassOrInterfaceType[
  pmd-java:typeIs('android.app.Activity') or
  pmd-java:typeIs('android.app.Application') or
  pmd-java:typeIs('android.app.Service')
]]]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class DummyActivity extends Activity {
    public void onCreate(Bundle bundle) {
        // missing call to super.onCreate(bundle)
        foo();
    }
}
]]>
        </example>
    </rule>

    <rule name="CallSuperLast"
          since="4.2.5"
          language="java"
          message="super should be called at the end of the method"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#callsuperlast">
        <description>
            Super should be called at the end of the method
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration[MethodDeclarator[
  @Image='finish' or
  @Image='onDestroy' or
  @Image='onPause' or
  @Image='onSaveInstanceState' or
  @Image='onStop' or
  @Image='onTerminate'
  ]]
   /Block/BlockStatement[last()]
    [not(Statement/StatementExpression/PrimaryExpression[./PrimaryPrefix[@SuperModifier='true']]/PrimarySuffix[@Image= ancestor::MethodDeclaration/MethodDeclarator/@Image])]
[ancestor::ClassOrInterfaceDeclaration[ExtendsList/ClassOrInterfaceType[
  pmd-java:typeIs('android.app.Activity') or
  pmd-java:typeIs('android.app.Application') or
  pmd-java:typeIs('android.app.Service')
]]]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class DummyActivity extends Activity {
    public void onPause() {
        foo();
        // missing call to super.onPause()
    }
}
]]>
        </example>
    </rule>

    <rule name="CheckSkipResult"
          language="java"
          since="5.0"
          message="Check the value returned by the skip() method of an InputStream to see if the requested number of bytes has been skipped."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.CheckSkipResultRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#checkskipresult">
        <description>
            The skip() method may skip a smaller number of bytes than requested. Check the returned value to find out if it was the case or not.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class Foo {

   private FileInputStream _s = new FileInputStream("file");

   public void skip(int n) throws IOException {
      _s.skip(n); // You are not sure that exactly n bytes are skipped
   }

   public void skipExactly(int n) throws IOException {
      while (n != 0) {
         long skipped = _s.skip(n);
         if (skipped == 0)
            throw new EOFException();
         n -= skipped;
      }
   }
]]>
        </example>
    </rule>

    <rule name="ClassCastExceptionWithToArray"
          language="java"
          since="3.4"
          message="This usage of the Collection.toArray() method will throw a ClassCastException."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#classcastexceptionwithtoarray">
        <description>
            When deriving an array of a specific class from your Collection, one should provide an array of
            the same class as the parameter of the toArray() method. Doing otherwise you will will result
            in a ClassCastException.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//CastExpression[Type/ReferenceType/ClassOrInterfaceType[@Image !=
"Object"]]/PrimaryExpression
[
 PrimaryPrefix/Name[ends-with(@Image, '.toArray')]
 and
 PrimarySuffix/Arguments[count(*) = 0]
and
count(PrimarySuffix) = 1
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
Collection c = new ArrayList();
Integer obj = new Integer(1);
c.add(obj);

    // this would trigger the rule (and throw a ClassCastException if executed)
Integer[] a = (Integer [])c.toArray();

   // this is fine and will not trigger the rule
Integer[] b = (Integer [])c.toArray(new Integer[c.size()]);
]]>
        </example>
    </rule>

    <rule name="CloneMethodMustBePublic"
          language="java"
          since="5.4.0"
          message="clone() method must be public if the class implements Cloneable"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#clonemethodmustbepublic">
        <description>
            The java Manual says "By convention, classes that implement this interface should override
            Object.clone (which is protected) with a public method."
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration[@Public='false']
  [MethodDeclarator/@Image = 'clone']
  [MethodDeclarator/FormalParameters/@ParameterCount = 0]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo implements Cloneable {
    @Override
    protected Object clone() throws CloneNotSupportedException { // Violation, must be public
    }
}

public class Foo implements Cloneable {
    @Override
    protected Foo clone() { // Violation, must be public
    }
}

public class Foo implements Cloneable {
    @Override
    public Object clone() // Ok
}
]]>
        </example>
    </rule>

    <rule name="CloneMethodMustImplementCloneable"
          language="java"
          since="1.9"
          message="clone() method should be implemented only if implementing Cloneable interface"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.CloneMethodMustImplementCloneableRule"
          typeResolution="true"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#clonemethodmustimplementcloneable">
        <description>
            The method clone() should only be implemented if the class implements the Cloneable interface with the exception of
            a final method that only throws CloneNotSupportedException.

            The rule can also detect, if the class implements or extends a Cloneable class.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class MyClass {
 public Object clone() throws CloneNotSupportedException {
  return foo;
 }
}
]]>
        </example>
    </rule>

    <rule name="CloneMethodReturnTypeMustMatchClassName"
          language="java"
          minimumLanguageVersion="1.5"
          since="5.4.0"
          message="The return type of the clone() method must be the class name when implements Cloneable"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#clonemethodreturntypemustmatchclassname">
        <description>
            If a class implements cloneable the return type of the method clone() must be the class name. That way, the caller
            of the clone method doesn't need to cast the returned clone to the correct type.

            Note: This is only possible with Java 1.5 or higher.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration
[
MethodDeclarator/@Image = 'clone'
and MethodDeclarator/FormalParameters/@ParameterCount = 0
and not (ResultType//ClassOrInterfaceType/@Image = ancestor::ClassOrInterfaceDeclaration[1]/@Image)
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo implements Cloneable {
    @Override
    protected Object clone() { // Violation, Object must be Foo
    }
}

public class Foo implements Cloneable {
    @Override
    public Foo clone() { //Ok
    }
}
]]>
        </example>
    </rule>

    <rule name="CloneThrowsCloneNotSupportedException"
          language="java"
          since="1.9"
          message="clone() method should throw CloneNotSupportedException"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#clonethrowsclonenotsupportedexception">
        <description>
            The method clone() should throw a CloneNotSupportedException.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration
[
MethodDeclarator/@Image = 'clone'
and count(MethodDeclarator/FormalParameters/*) = 0
and count(NameList/Name[contains
(@Image,'CloneNotSupportedException')]) = 0
]
[
../../../../ClassOrInterfaceDeclaration[@Final = 'false']
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class MyClass implements Cloneable{
    public Object clone() { // will cause an error
         MyClass clone = (MyClass)super.clone();
         return clone;
    }
}
]]>
        </example>
    </rule>

    <rule name="CloseResource"
          since="1.2.2"
          message="Ensure that resources like this {0} object are closed after use"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.CloseResourceRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#closeresource">
        <description>
            Ensure that resources (like Connection, Statement, and ResultSet objects) are always closed after use.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class Bar {
  public void foo() {
    Connection c = pool.getConnection();
    try {
      // do stuff
    } catch (SQLException ex) {
     // handle exception
    } finally {
      // oops, should close the connection using 'close'!
      // c.close();
    }
  }
}
]]>
        </example>
    </rule>

    <rule name="CompareObjectsWithEquals"
          since="3.2"
          message="Use equals() to compare object references."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.CompareObjectsWithEqualsRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#compareobjectswithequals">
        <description>
            Use equals() to compare object references; avoid comparing them with ==.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
class Foo {
  boolean bar(String a, String b) {
    return a == b;
  }
}

]]>
        </example>
    </rule>

    <rule name="ConstructorCallsOverridableMethod"
          since="1.04"
          message="Overridable {0} called during object construction"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.ConstructorCallsOverridableMethodRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#constructorcallsoverridablemethod">
        <description>
            Calling overridable methods during construction poses a risk of invoking methods on an incompletely
            constructed object and can be difficult to debug.
            It may leave the sub-class unable to construct its superclass or forced to replicate the construction
            process completely within itself, losing the ability to call super().  If the default constructor
            contains a call to an overridable method, the subclass may be completely uninstantiable.   Note that
            this includes method calls throughout the control flow graph - i.e., if a constructor Foo() calls a
            private method bar() that calls a public method buz(), this denotes a problem.
        </description>
        <priority>1</priority>
        <example>
            <![CDATA[
public class SeniorClass {
  public SeniorClass(){
      toString(); //may throw NullPointerException if overridden
  }
  public String toString(){
    return "IAmSeniorClass";
  }
}
public class JuniorClass extends SeniorClass {
  private String name;
  public JuniorClass(){
    super(); //Automatic call leads to NullPointerException
    name = "JuniorClass";
  }
  public String toString(){
    return name.toUpperCase();
  }
}
]]>
        </example>
    </rule>

    <rule name="DataflowAnomalyAnalysis"
          since="3.9"
          message="Found ''{0}''-anomaly for variable ''{1}'' (lines ''{2}''-''{3}'')."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.DataflowAnomalyAnalysisRule"
          dfa="true"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#dataflowanomalyanalysis">
        <description>The dataflow analysis tracks local definitions, undefinitions and references to variables on different paths on the data flow.
            From those informations there can be found various problems.

            1. UR - Anomaly: There is a reference to a variable that was not defined before. This is a bug and leads to an error.
            2. DU - Anomaly: A recently defined variable is undefined. These anomalies may appear in normal source text.
            3. DD - Anomaly: A recently defined variable is redefined. This is ominous but don't have to be a bug.
        </description>
        <priority>5</priority>
        <example>
            <![CDATA[
public void foo() {
  int buz = 5;
  buz = 6; // redefinition of buz -> dd-anomaly
  foo(buz);
  buz = 2;
} // buz is undefined when leaving scope -> du-anomaly
]]>
        </example>
    </rule>

    <rule name="DoNotCallGarbageCollectionExplicitly"
          language="java"
          since="4.2"
          message="Do not explicitly trigger a garbage collection."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donotcallgarbagecollectionexplicitly">
        <description>
            Calls to System.gc(), Runtime.getRuntime().gc(), and System.runFinalization() are not advised. Code should have the
            same behavior whether the garbage collection is disabled using the option -Xdisableexplicitgc or not.
            Moreover, "modern" jvms do a very good job handling garbage collections. If memory usage issues unrelated to memory
            leaks develop within an application, it should be dealt with JVM options rather than within the code itself.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//Name[
(starts-with(@Image, 'System.') and
(starts-with(@Image, 'System.gc') or
starts-with(@Image, 'System.runFinalization'))) or
(
starts-with(@Image,'Runtime.getRuntime') and
../../PrimarySuffix[ends-with(@Image,'gc')]
)
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class GCCall {
    public GCCall() {
        // Explicit gc call !
        System.gc();
    }

    public void doSomething() {
        // Explicit gc call !
        Runtime.getRuntime().gc();
    }

    public explicitGCcall() {
        // Explicit gc call !
        System.gc();
    }

    public void doSomething() {
        // Explicit gc call !
        Runtime.getRuntime().gc();
    }
}
]]>
        </example>
    </rule>

    <rule name="DoNotCallSystemExit"
          language="java"
          since="4.1"
          message="System.exit() should not be used in J2EE/JEE apps"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donotcallsystemexit">
        <description>
            Web applications should not call System.exit(), since only the web container or the
            application server should stop the JVM. This rule also checks for the equivalent call Runtime.getRuntime().exit().
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//Name[
    starts-with(@Image,'System.exit')
    or
    (starts-with(@Image,'Runtime.getRuntime') and ../../PrimarySuffix[ends-with(@Image,'exit')])
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public void bar() {
    System.exit(0);                 // never call this when running in an application server!
}
public void foo() {
    Runtime.getRuntime().exit(0);   // never stop the JVM manually, the container will do this.
}
]]>
        </example>
    </rule>

    <rule name="DoNotExtendJavaLangThrowable"
          language="java"
          since="6.0.0"
          message="Exceptions should not extend java.lang.Throwable"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donotextendjavalangthrowable">
        <description>
            Extend Exception or RuntimeException instead of Throwable.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//ClassOrInterfaceDeclaration/ExtendsList/ClassOrInterfaceType
  [@Image="Throwable" or @Image="java.lang.Throwable"]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo extends Throwable { }
]]>
        </example>
    </rule>

    <rule name="DoNotHardCodeSDCard"
          since="4.2.6"
          language="java"
          message="Do not hardcode /sdcard."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donothardcodesdcard">
        <description>
            Use Environment.getExternalStorageDirectory() instead of "/sdcard"
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//Literal[starts-with(@Image,'"/sdcard')]</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class MyActivity extends Activity {
    protected void foo() {
        String storageLocation = "/sdcard/mypackage";   // hard-coded, poor approach

       storageLocation = Environment.getExternalStorageDirectory() + "/mypackage"; // preferred approach
    }
}
]]>
        </example>
    </rule>

    <rule name="DoNotThrowExceptionInFinally"
          language="java"
          since="4.2"
          message="A throw statement in a finally block makes the control flow hard to understand."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#donotthrowexceptioninfinally">
        <description>
            Throwing exceptions within a 'finally' block is confusing since they may mask other exceptions
            or code defects.
            Note: This is a PMD implementation of the Lint4j rule "A throw in a finally block"
        </description>
        <priority>4</priority>
        <properties>
            <property name="xpath">
                <value>//FinallyStatement[descendant::ThrowStatement]</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    public void bar() {
        try {
            // Here do some stuff
        } catch( Exception e) {
            // Handling the issue
        } finally {
            // is this really a good idea ?
            throw new Exception();
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="DontImportSun"
          since="1.5"
          message="Avoid importing anything from the 'sun.*' packages"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.DontImportSunRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#dontimportsun">
        <description>
            Avoid importing anything from the 'sun.*' packages.  These packages are not portable and are likely to change.
        </description>
        <priority>4</priority>
        <example>
            <![CDATA[
import sun.misc.foo;
public class Foo {}
]]>
        </example>
    </rule>

    <rule name="DontUseFloatTypeForLoopIndices"
          language="java"
          since="4.3"
          message="Don't use floating point for loop indices. If you must use floating point, use double."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#dontusefloattypeforloopindices">
        <description>
            Don't use floating point for loop indices. If you must use floating point, use double
            unless you're certain that float provides enough precision and you have a compelling
            performance need (space or time).
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//ForStatement/ForInit/LocalVariableDeclaration
/Type/PrimitiveType[@Image="float"]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Count {
  public static void main(String[] args) {
    final int START = 2000000000;
    int count = 0;
    for (float f = START; f < START + 50; f++)
      count++;
      //Prints 0 because (float) START == (float) (START + 50).
      System.out.println(count);
      //The termination test misbehaves due to floating point granularity.
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyCatchBlock"
          language="java"
          since="0.1"
          message="Avoid empty catch blocks"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptycatchblock">
        <description>
            Empty Catch Block finds instances where an exception is caught, but nothing is done.
            In most circumstances, this swallows an exception which should either be acted on
            or reported.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//CatchStatement
 [count(Block/BlockStatement) = 0 and ($allowCommentedBlocks != 'true' or Block/@containsComment = 'false')]
 [FormalParameter/Type/ReferenceType
   /ClassOrInterfaceType[@Image != 'InterruptedException' and @Image != 'CloneNotSupportedException']
 ]
 [FormalParameter/VariableDeclaratorId[not(matches(@Image, $allowExceptionNameRegex))]]
]]>
                </value>
            </property>
            <property name="allowCommentedBlocks" type="Boolean" description="Empty blocks containing comments will be skipped" value="false"/>
            <property name="allowExceptionNameRegex" type="String" description="Empty blocks catching exceptions with names matching this regular expression will be skipped" value="^(ignored|expected)$"/>
        </properties>
        <example>
            <![CDATA[
public void doSomething() {
    try {
        FileInputStream fis = new FileInputStream("/tmp/bugger");
    } catch (IOException ioe) {
        // not good
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyFinalizer"
          language="java"
          since="1.5"
          message="Avoid empty finalize methods"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyfinalizer">
        <description>
            Empty finalize methods serve no purpose and should be removed. Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration[MethodDeclarator[@Image='finalize'][not(FormalParameters/*)]]
  /Block[count(*)=0]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
   protected void finalize() {}
}
]]>
        </example>
    </rule>

    <rule name="EmptyFinallyBlock"
          language="java"
          since="0.4"
          message="Avoid empty finally blocks"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyfinallyblock">
        <description>
            Empty finally blocks serve no purpose and should be removed.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//FinallyStatement[count(Block/BlockStatement) = 0]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    public void bar() {
        try {
            int x=2;
        } finally {
            // empty!
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyIfStmt"
          language="java"
          since="0.1"
          message="Avoid empty 'if' statements"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyifstmt">
        <description>
            Empty If Statement finds instances where a condition is checked but nothing is done about it.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//IfStatement/Statement
 [EmptyStatement or Block[count(*) = 0]]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
 void bar(int x) {
  if (x == 0) {
   // empty!
  }
 }
}
]]>
        </example>
    </rule>

    <rule name="EmptyInitializer"
          language="java"
          since="5.0"
          message="Empty initializer was found"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyinitializer">
        <description>
            Empty initializers serve no purpose and should be removed.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//Initializer/Block[count(*)=0]</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {

   static {} // Why ?

   {} // Again, why ?

}
]]>
        </example>
    </rule>

    <rule name="EmptyStatementBlock"
          language="java"
          since="5.0"
          message="Avoid empty block statements."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptystatementblock">
        <description>
            Empty block statements serve no purpose and should be removed.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//BlockStatement/Statement/Block[count(*) = 0]</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {

   private int _bar;

   public void setBar(int bar) {
      { _bar = bar; } // Why not?
      {} // But remove this.
   }

}
]]>
        </example>
    </rule>

    <rule name="EmptyStatementNotInLoop"
          language="java"
          since="1.5"
          message="An empty statement (semicolon) not part of a loop"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptystatementnotinloop">
        <description>
            An empty statement (or a semicolon by itself) that is not used as the sole body of a 'for'
            or 'while' loop is probably a bug.  It could also be a double semicolon, which has no purpose
            and should be removed.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//EmptyStatement
 [not(
       ../../../ForStatement
       or ../../../WhileStatement
       or ../../../BlockStatement/ClassOrInterfaceDeclaration
       or ../../../../../../ForStatement/Statement[1]
        /Block[1]/BlockStatement[1]/Statement/EmptyStatement
       or ../../../../../../WhileStatement/Statement[1]
        /Block[1]/BlockStatement[1]/Statement/EmptyStatement)
 ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public void doit() {
      // this is probably not what you meant to do
      ;
      // the extra semicolon here this is not necessary
      System.out.println("look at the extra semicolon");;
}
]]>
        </example>
    </rule>

    <rule name="EmptySwitchStatements"
          language="java"
          since="1.0"
          message="Avoid empty switch statements"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptyswitchstatements">
        <description>
            Empty switch statements serve no purpose and should be removed.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//SwitchStatement[count(*) = 1]</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public void bar() {
    int x = 2;
    switch (x) {
        // once there was code here
        // but it's been commented out or something
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptySynchronizedBlock"
          language="java"
          since="1.3"
          message="Avoid empty synchronized blocks"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptysynchronizedblock">
        <description>
            Empty synchronized blocks serve no purpose and should be removed.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//SynchronizedStatement/Block[1][count(*) = 0]</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    public void bar() {
        synchronized (this) {
            // empty!
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyTryBlock"
          language="java"
          since="0.4"
          message="Avoid empty try blocks"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptytryblock">
        <description>
            Avoid empty try blocks - what's the point?
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//TryStatement[not(ResourceSpecification)]/Block[1][count(*) = 0]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    public void bar() {
        try {
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="EmptyWhileStmt"
          language="java"
          since="0.2"
          message="Avoid empty 'while' statements"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#emptywhilestmt">
        <description>
            Empty While Statement finds all instances where a while statement does nothing.
            If it is a timing loop, then you should use Thread.sleep() for it; if it is
            a while loop that does a lot in the exit expression, rewrite it to make it clearer.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//WhileStatement/Statement[./Block[count(*) = 0]  or ./EmptyStatement]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
void bar(int a, int b) {
    while (a == b) {
        // empty!
    }
}
 ]]>
        </example>
    </rule>

    <rule name="EqualsNull"
          language="java"
          since="1.9"
          message="Avoid using equals() to compare against null"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#equalsnull">
        <description>
            Tests for null should not use the equals() method. The '==' operator should be used instead.
        </description>
        <priority>1</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//PrimaryExpression
  [
    PrimaryPrefix[Name[ends-with(@Image, 'equals')]]
      [following-sibling::node()/Arguments/ArgumentList[count(Expression)=1]
          /Expression/PrimaryExpression/PrimaryPrefix/Literal/NullLiteral]

    or

    PrimarySuffix[ends-with(@Image, 'equals')]
      [following-sibling::node()/Arguments/ArgumentList[count(Expression)=1]
          /Expression/PrimaryExpression/PrimaryPrefix/Literal/NullLiteral]

  ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
String x = "foo";

if (x.equals(null)) {   // bad form
    doSomething();
}

if (x == null) {        // preferred
    doSomething();
}
]]>
        </example>
    </rule>

    <rule name="FinalizeDoesNotCallSuperFinalize"
          language="java"
          since="1.5"
          message="Last statement in finalize method should be a call to super.finalize()"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#finalizedoesnotcallsuperfinalize">
        <description>
            If the finalize() is implemented, its last action should be to call super.finalize. Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <!-- in English: a method declaration of finalize(), with no arguments, containing
                    a block whose last statement is NOT a call to super.finalize -->
                    <![CDATA[
//MethodDeclaration[MethodDeclarator[@Image='finalize'][not(FormalParameters/*)]]
   /Block
      /BlockStatement[last()]
      [not(Statement/StatementExpression/PrimaryExpression
            [./PrimaryPrefix[@SuperModifier='true']]
            [./PrimarySuffix[@Image='finalize']]
          )
      ]
      [not(Statement/TryStatement/FinallyStatement
       /Block/BlockStatement/Statement/StatementExpression/PrimaryExpression
            [./PrimaryPrefix[@SuperModifier='true']]
            [./PrimarySuffix[@Image='finalize']]
          )
      ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
protected void finalize() {
    something();
    // neglected to call super.finalize()
}
]]>
        </example>
    </rule>

    <rule name="FinalizeOnlyCallsSuperFinalize"
          language="java"
          since="1.5"
          message="Finalize should do something besides just calling super.finalize()"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#finalizeonlycallssuperfinalize">
        <description>
            If the finalize() is implemented, it should do something besides just calling super.finalize(). Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration[MethodDeclarator[@Image="finalize"][not(FormalParameters/*)]]
   /Block[count(BlockStatement)=1]
     /BlockStatement[
       Statement/StatementExpression/PrimaryExpression
       [./PrimaryPrefix[@SuperModifier='true']]
       [./PrimarySuffix[@Image='finalize']]
     ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
protected void finalize() {
    super.finalize();
}
]]>
        </example>
    </rule>

    <rule name="FinalizeOverloaded"
          language="java"
          since="1.5"
          message="Finalize methods should not be overloaded"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#finalizeoverloaded">
        <description>
            Methods named finalize() should not have parameters.  It is confusing and most likely an attempt to
            overload Object.finalize(). It will not be called by the VM.

            Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration
 /MethodDeclarator[@Image='finalize'][FormalParameters[count(*)>0]]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    // this is confusing and probably a bug
    protected void finalize(int a) {
    }
}
]]>
        </example>
    </rule>

    <rule name="FinalizeShouldBeProtected"
          language="java"
          since="1.1"
          message="If you override finalize(), make it protected"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#finalizeshouldbeprotected">
        <description>
            When overriding the finalize(), the new method should be set as protected.  If made public,
            other classes may invoke it at inappropriate times.

            Note that Oracle has declared Object.finalize() as deprecated since JDK 9.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration[@Protected="false"]
  /MethodDeclarator[@Image="finalize"]
  [not(FormalParameters/*)]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public void finalize() {
    // do something
}
]]>
        </example>
    </rule>

    <rule name="IdempotentOperations"
          since="2.0"
          message="Avoid idempotent operations (like assigning a variable to itself)."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.IdempotentOperationsRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#idempotentoperations">
        <description>
            Avoid idempotent operations - they have no effect.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class Foo {
 public void bar() {
  int x = 2;
  x = x;
 }
}
]]>
        </example>
    </rule>

    <rule name="ImportFromSamePackage"
          since="1.02"
          message="No need to import a type that lives in the same package"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.ImportFromSamePackageRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#importfromsamepackage">
        <description>
            There is no need to import a type that lives in the same package.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
package foo;

import foo.Buz;     // no need for this
import foo.*;       // or this

public class Bar{}
]]>
        </example>
    </rule>

    <rule name="InstantiationToGetClass"
          language="java"
          since="2.0"
          message="Avoid instantiating an object just to call getClass() on it; use the .class public member instead"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#instantiationtogetclass">
        <description>
            Avoid instantiating an object just to call getClass() on it; use the .class public member instead.
        </description>
        <priority>4</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//PrimarySuffix
 [@Image='getClass']
 [parent::PrimaryExpression
  [PrimaryPrefix/AllocationExpression]
  [count(PrimarySuffix) = 2]
 ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
// replace this
Class c = new String().getClass();

// with this:
Class c = String.class;
]]>
        </example>
    </rule>

    <rule name="InvalidSlf4jMessageFormat"
          language="java"
          since="5.5.0"
          message="Invalid message format"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.InvalidSlf4jMessageFormatRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#invalidslf4jmessageformat">
        <description>
            Check for messages in slf4j loggers with non matching number of arguments and placeholders.
        </description>
        <priority>5</priority>
        <example>
            <![CDATA[
LOGGER.error("forget the arg {}");
LOGGER.error("too many args {}", "arg1", "arg2");
LOGGER.error("param {}", "arg1", new IllegalStateException("arg")); //The exception is shown separately, so is correct.
]]>
        </example>
    </rule>

    <rule name="JumbledIncrementer"
          language="java"
          since="1.0"
          message="Avoid modifying an outer loop incrementer in an inner loop for update expression"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#jumbledincrementer">
        <description>
            Avoid jumbled loop incrementers - its usually a mistake, and is confusing even if intentional.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value><![CDATA[
//ForStatement
  [
    ForUpdate/StatementExpressionList/StatementExpression/PostfixExpression/PrimaryExpression/PrimaryPrefix/Name/@Image
    =
    ancestor::ForStatement/ForInit//VariableDeclaratorId/@Image
  ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class JumbledIncrementerRule1 {
    public void foo() {
        for (int i = 0; i < 10; i++) {          // only references 'i'
            for (int k = 0; k < 20; i++) {      // references both 'i' and 'k'
                System.out.println("Hello");
            }
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="JUnitSpelling"
          language="java"
          since="1.0"
          message="You may have misspelled a JUnit framework method (setUp or tearDown)"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#junitspelling">
        <description>
            Some JUnit framework methods are easy to misspell.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclarator[(not(@Image = 'setUp')
 and translate(@Image, 'SETuP', 'setUp') = 'setUp')
 or (not(@Image = 'tearDown')
 and translate(@Image, 'TEARdOWN', 'tearDown') = 'tearDown')]
 [FormalParameters[count(*) = 0]]
[ancestor::ClassOrInterfaceDeclaration[//ClassOrInterfaceType[pmd-java:typeIs('junit.framework.TestCase')]
    or //MarkerAnnotation/Name[
        pmd-java:typeIs('org.junit.Test')
        or pmd-java:typeIs('org.junit.jupiter.api.Test') or pmd-java:typeIs('org.junit.jupiter.api.RepeatedTest')
        or pmd-java:typeIs('org.junit.jupiter.api.TestFactory') or pmd-java:typeIs('org.junit.jupiter.api.TestTemplate')
        or pmd-java:typeIs('org.junit.jupiter.params.ParameterizedTest')
    ]
]]]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
import junit.framework.*;

public class Foo extends TestCase {
    public void setup() {}    // oops, should be setUp
    public void TearDown() {} // oops, should be tearDown
}
]]>
        </example>
    </rule>

    <rule name="JUnitStaticSuite"
          language="java"
          since="1.0"
          message="You have a suite() method that is not both public and static, so JUnit won't call it to get your TestSuite.  Is that what you wanted to do?"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          typeResolution="true"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#junitstaticsuite">
        <description>
            The suite() method in a JUnit test needs to be both public and static.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration[not(@Static='true') or not(@Public='true')]
[MethodDeclarator/@Image='suite']
[MethodDeclarator/FormalParameters/@ParameterCount=0]
[ancestor::ClassOrInterfaceDeclaration[//ClassOrInterfaceType[pmd-java:typeIs('junit.framework.TestCase')]
    or //MarkerAnnotation/Name[
        pmd-java:typeIs('org.junit.Test')
        or pmd-java:typeIs('org.junit.jupiter.api.Test') or pmd-java:typeIs('org.junit.jupiter.api.RepeatedTest')
        or pmd-java:typeIs('org.junit.jupiter.api.TestFactory') or pmd-java:typeIs('org.junit.jupiter.api.TestTemplate')
        or pmd-java:typeIs('org.junit.jupiter.params.ParameterizedTest')
    ]
]]]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
import junit.framework.*;

public class Foo extends TestCase {
    public void suite() {}         // oops, should be static
    private static void suite() {} // oops, should be public
}
]]>
        </example>
    </rule>

    <rule name="LoggerIsNotStaticFinal"
          language="java"
          since="2.0"
          message="The Logger variable declaration does not contain the static and final modifiers"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#loggerisnotstaticfinal">
        <description>
            In most cases, the Logger reference can be declared as static and final.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//VariableDeclarator
 [parent::FieldDeclaration]
 [../Type/ReferenceType
  /ClassOrInterfaceType[@Image='Logger']
   and
  (..[@Final='false'] or ..[@Static = 'false'] ) ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo{
    Logger log = Logger.getLogger(Foo.class.getName());                 // not recommended

    static final Logger log = Logger.getLogger(Foo.class.getName());    // preferred approach
}
]]>
        </example>
    </rule>

    <rule name="MethodWithSameNameAsEnclosingClass"
          since="1.5"
          message="Classes should not have non-constructor methods with the same name as the class"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.MethodWithSameNameAsEnclosingClassRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#methodwithsamenameasenclosingclass">
        <description>
            Non-constructor methods should not have the same name as the enclosing class.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class MyClass {

    public MyClass() {}         // this is OK because it is a constructor

    public void MyClass() {}    // this is bad because it is a method
}
]]>
        </example>
    </rule>

    <rule name="MisplacedNullCheck"
          language="java"
          since="3.5"
          message="The null check here is misplaced; if the variable is null there will be a NullPointerException"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#misplacednullcheck">
        <description>
            The null check here is misplaced. If the variable is null a NullPointerException will be thrown.
            Either the check is useless (the variable will never be "null") or it is incorrect.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//Expression
    /*[self::ConditionalOrExpression or self::ConditionalAndExpression]
    /descendant::PrimaryExpression/PrimaryPrefix
    /Name[starts-with(@Image,
        concat(ancestor::PrimaryExpression/following-sibling::EqualityExpression
            [./PrimaryExpression/PrimaryPrefix/Literal/NullLiteral]
            /PrimaryExpression/PrimaryPrefix
            /Name[count(../../PrimarySuffix)=0]/@Image,".")
        )
     ]
     [count(ancestor::ConditionalAndExpression/EqualityExpression
            [@Image='!=']
            [./PrimaryExpression/PrimaryPrefix/Literal/NullLiteral]
            [starts-with(following-sibling::*/PrimaryExpression/PrimaryPrefix/Name/@Image,
                concat(./PrimaryExpression/PrimaryPrefix/Name/@Image, '.'))]
      ) = 0
     ]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    void bar() {
        if (a.equals(baz) && a != null) {}
        }
}
]]>
        </example>
        <example>
            <![CDATA[
public class Foo {
    void bar() {
        if (a.equals(baz) || a == null) {}
    }
}
]]>
        </example>
    </rule>

    <rule name="MissingBreakInSwitch"
          language="java"
          since="3.0"
          message="A switch statement does not contain a break"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#missingbreakinswitch">
        <description>
            Switch statements without break or return statements for each case option
            may indicate problematic behaviour. Empty cases are ignored as these indicate an intentional fall-through.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//SwitchStatement
[(count(.//BreakStatement)
 + count(BlockStatement//Statement/ReturnStatement)
 + count(BlockStatement//Statement/ContinueStatement)
 + count(BlockStatement//Statement/ThrowStatement)
 + count(BlockStatement//Statement/IfStatement[@Else='true' and Statement[2][ReturnStatement|ContinueStatement|ThrowStatement]]/Statement[1][ReturnStatement|ContinueStatement|ThrowStatement])
 + count(SwitchLabel[name(following-sibling::node()) = 'SwitchLabel'])
 + count(SwitchLabel[count(following-sibling::node()) = 0])
  < count (SwitchLabel))]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public void bar(int status) {
    switch(status) {
      case CANCELLED:
        doCancelled();
        // break; hm, should this be commented out?
      case NEW:
        doNew();
        // is this really a fall-through?
      case REMOVED:
        doRemoved();
        // what happens if you add another case after this one?
      case OTHER: // empty case - this is interpreted as an intentional fall-through
      case ERROR:
        doErrorHandling();
        break;
    }
}
]]>
        </example>
    </rule>

    <rule name="MissingSerialVersionUID"
          language="java"
          since="3.0"
          message="Classes implementing Serializable should set a serialVersionUID"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          typeResolution="true"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#missingserialversionuid">
        <description>
            Serializable classes should provide a serialVersionUID field.
            The serialVersionUID field is also needed for abstract base classes. Each individual class in the inheritance
            chain needs an own serialVersionUID field. See also [Should an abstract class have a serialVersionUID](https://stackoverflow.com/questions/893259/should-an-abstract-class-have-a-serialversionuid).
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//ClassOrInterfaceDeclaration
    [@Interface = 'false']
    [count(ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration
        /FieldDeclaration/VariableDeclarator/VariableDeclaratorId[@Image='serialVersionUID']) = 0]
    [(ImplementsList | ExtendsList)/ClassOrInterfaceType[pmd-java:typeIs('java.io.Serializable')]]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo implements java.io.Serializable {
    String name;
    // Define serialization id to avoid serialization related bugs
    // i.e., public static final long serialVersionUID = 4328743;
}
]]>
        </example>
    </rule>

    <rule name="MissingStaticMethodInNonInstantiatableClass"
          language="java"
          since="3.0"
          message="Class cannot be instantiated and does not provide any static methods or fields"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#missingstaticmethodinnoninstantiatableclass">
        <description>
            A class that has private constructors and does not have any static methods or fields cannot be used.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//ClassOrInterfaceDeclaration[@Nested='false']
[
  (
    ./ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/ConstructorDeclaration
    and
    count(./ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/ConstructorDeclaration) = count(./ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/ConstructorDeclaration[@Private='true'])
  )
  and
  not(.//MethodDeclaration[@Static='true'])
  and
  not(.//FieldDeclaration[@Private='false'][@Static='true'])
  and
  not(.//ClassOrInterfaceDeclaration[@Nested='true']
           [@Public='true']
           [@Static='true']
           [not(./ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/ConstructorDeclaration) or ./ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/ConstructorDeclaration[@Public='true']]
           [./ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/MethodDeclaration
                [@Public='true']
                [./ResultType/Type/ReferenceType/ClassOrInterfaceType
                    [@Image = //ClassOrInterfaceDeclaration[@Nested='false']/@Image]
                ]
            ]
        )
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
// This class is unusable, since it cannot be
// instantiated (private constructor),
// and no static method can be called.

public class Foo {
  private Foo() {}
  void foo() {}
}

]]>
        </example>
    </rule>

    <rule name="MoreThanOneLogger"
          since="2.0"
          message="Class contains more than one logger."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.MoreThanOneLoggerRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#morethanonelogger">
        <description>
            Normally only one logger is used in each class.
        </description>
        <priority>2</priority>
        <example>
            <![CDATA[
public class Foo {
    Logger log = Logger.getLogger(Foo.class.getName());
    // It is very rare to see two loggers on a class, normally
    // log information is multiplexed by levels
    Logger log2= Logger.getLogger(Foo.class.getName());
}
]]>
        </example>
    </rule>

    <rule name="NonCaseLabelInSwitchStatement"
          language="java"
          since="1.5"
          message="A non-case label was present in a switch statement"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#noncaselabelinswitchstatement">
        <description>
            A non-case label (e.g. a named break/continue label) was present in a switch statement.
            This legal, but confusing. It is easy to mix up the case labels and the non-case labels.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//SwitchStatement//BlockStatement/Statement/LabeledStatement</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
  void bar(int a) {
   switch (a) {
     case 1:
       // do something
       break;
     mylabel: // this is legal, but confusing!
       break;
     default:
       break;
    }
  }
}
]]>
        </example>
    </rule>

    <rule name="NonStaticInitializer"
          language="java"
          since="1.5"
          message="Non-static initializers are confusing"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#nonstaticinitializer">
        <description>
            A non-static initializer block will be called any time a constructor is invoked (just prior to
            invoking the constructor).  While this is a valid language construct, it is rarely used and is
            confusing.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//Initializer[@Static='false']
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class MyClass {
  // this block gets run before any call to a constructor
  {
    System.out.println("I am about to construct myself");
  }
}
]]>
        </example>
    </rule>

    <rule name="NullAssignment"
          since="1.02"
          message="Assigning an Object to null is a code smell.  Consider refactoring."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.NullAssignmentRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#nullassignment">
        <description>
            Assigning a "null" to a variable (outside of its declaration) is usually bad form.  Sometimes, this type
            of assignment is an indication that the programmer doesn't completely understand what is going on in the code.

            NOTE: This sort of assignment may used in some cases to dereference objects and encourage garbage collection.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public void bar() {
  Object x = null; // this is OK
  x = new Object();
     // big, complex piece of code here
  x = null; // this is not required
     // big, complex piece of code here
}
]]>
        </example>
    </rule>

    <rule name="OverrideBothEqualsAndHashcode"
          language="java"
          since="0.4"
          message="Ensure you override both equals() and hashCode()"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.OverrideBothEqualsAndHashcodeRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#overridebothequalsandhashcode">
        <description>
            Override both public boolean Object.equals(Object other), and public int Object.hashCode(), or override neither.  Even if you are inheriting a hashCode() from a parent class, consider implementing hashCode and explicitly delegating to your superclass.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class Bar {        // poor, missing a hashcode() method
    public boolean equals(Object o) {
      // do some comparison
    }
}

public class Baz {        // poor, missing an equals() method
    public int hashCode() {
      // return some hash value
    }
}

public class Foo {        // perfect, both methods provided
    public boolean equals(Object other) {
      // do some comparison
    }
    public int hashCode() {
      // return some hash value
    }
}
]]>
        </example>
    </rule>

    <rule name="ProperCloneImplementation"
          language="java"
          since="1.4"
          message="Object clone() should be implemented with super.clone()"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#propercloneimplementation">
        <description>
            Object clone() should be implemented with super.clone().
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclarator
[@Image = 'clone']
[count(FormalParameters/*) = 0]
[count(../Block//*[
    (self::AllocationExpression) and
    (./ClassOrInterfaceType/@Image = ancestor::
ClassOrInterfaceDeclaration[1]/@Image)
  ])> 0
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
class Foo{
    public Object clone(){
        return new Foo(); // This is bad
    }
}
]]>
        </example>
    </rule>

    <rule name="ProperLogger"
          language="java"
          since="3.3"
          message="Logger should be defined private static final and have the correct class"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#properlogger">
        <description>
            A logger should normally be defined private static final and be associated with the correct class.
            Private final Log log; is also allowed for rare cases where loggers need to be passed around,
            with the restriction that the logger needs to be passed into the constructor.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//ClassOrInterfaceBodyDeclaration[FieldDeclaration//ClassOrInterfaceType[@Image='Log']
 and
 not(FieldDeclaration[@Final='true'][@Static='true'][@Private='true'][.//VariableDeclaratorId[@Image=$staticLoggerName]]
 and
 //ArgumentList//ClassOrInterfaceType[@Image = ancestor::ClassOrInterfaceDeclaration/@Image or @Image = ancestor::EnumDeclaration/@Image])
 and
 not(FieldDeclaration[@Final='true'][@Private='true'][.//VariableDeclaratorId[@Image='log']]
 [count(.//VariableInitializer)=0]
 [ancestor::ClassOrInterfaceBody//StatementExpression[.//PrimaryExpression/descendant::*[@Image='log']][count(.//AllocationExpression)=0]]
 )]
]]>
                </value>
            </property>
            <property name="staticLoggerName" type="String" description="Name of the static Logger variable" value="LOG"/>
        </properties>
        <example>
            <![CDATA[
public class Foo {

    private static final Log LOG = LogFactory.getLog(Foo.class);    // proper way

    protected Log LOG = LogFactory.getLog(Testclass.class);         // wrong approach
}
]]>
        </example>
    </rule>

    <rule name="ReturnEmptyArrayRatherThanNull"
          language="java"
          since="4.2"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          message="Return an empty array rather than 'null'."
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#returnemptyarrayratherthannull">
        <description>
            For any method that returns an array, it is a better to return an empty array rather than a
            null reference. This removes the need for null checking all results and avoids inadvertent
            NullPointerExceptions.
        </description>
        <priority>1</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclaration
[
(./ResultType/Type[@ArrayType='true'])
and
(./Block/BlockStatement/Statement/ReturnStatement/Expression/PrimaryExpression/PrimaryPrefix/Literal/NullLiteral)
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Example {
    // Not a good idea...
    public int[] badBehavior() {
        // ...
        return null;
    }

    // Good behavior
    public String[] bonnePratique() {
        //...
        return new String[0];
    }
}
]]>
        </example>
    </rule>

    <rule name="ReturnFromFinallyBlock"
          language="java"
          since="1.05"
          message="Avoid returning from a finally block"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#returnfromfinallyblock">
        <description>
            Avoid returning from a finally block, this can discard exceptions.
        </description>
        <priority>3</priority>
        <properties>
            <property name="version" value="2.0"/>
            <property name="xpath">
                <value>//FinallyStatement//ReturnStatement except //FinallyStatement//(MethodDeclaration|LambdaExpression)//ReturnStatement</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Bar {
    public String foo() {
        try {
            throw new Exception( "My Exception" );
        } catch (Exception e) {
            throw e;
        } finally {
            return "A. O. K."; // return not recommended here
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="SimpleDateFormatNeedsLocale"
          language="java"
          since="2.0"
          message="When instantiating a SimpleDateFormat object, specify a Locale"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#simpledateformatneedslocale">
        <description>
            Be sure to specify a Locale when creating SimpleDateFormat instances to ensure that locale-appropriate
            formatting is used.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//AllocationExpression
 [ClassOrInterfaceType[@Image='SimpleDateFormat']]
 [Arguments[@ArgumentCount=1]]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
  // Should specify Locale.US (or whatever)
  private SimpleDateFormat sdf = new SimpleDateFormat("pattern");
}
]]>
        </example>
    </rule>

    <rule name="SingleMethodSingleton"
          since="5.4"
          message="Class contains multiple getInstance methods. Please review."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.SingleMethodSingletonRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#singlemethodsingleton">
        <description>
            Some classes contain overloaded getInstance. The problem with overloaded getInstance methods
            is that the instance created using the overloaded method is not cached and so,
            for each call and new objects will be created for every invocation.
        </description>
        <priority>2</priority>
        <example>
            <![CDATA[
public class Singleton {

    private static Singleton singleton = new Singleton( );

    private Singleton(){ }

    public static Singleton getInstance( ) {
        return singleton;
    }

    public static Singleton getInstance(Object obj){
        Singleton singleton = (Singleton) obj;
        return singleton;           //violation
    }
}
]]>
        </example>
    </rule>

    <rule name="SingletonClassReturningNewInstance"
          since="5.4"
          message="getInstance method always creates a new object and hence does not comply to Singleton Design Pattern behaviour. Please review"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.SingletonClassReturningNewInstanceRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#singletonclassreturningnewinstance">
        <description>
            Some classes contain overloaded getInstance. The problem with overloaded getInstance methods
            is that the instance created using the overloaded method is not cached and so,
            for each call and new objects will be created for every invocation.
        </description>
        <priority>2</priority>
        <example>
            <![CDATA[
class Singleton {
    private static Singleton instance = null;
    public static Singleton getInstance() {
        synchronized(Singleton.class) {
            return new Singleton();
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="StaticEJBFieldShouldBeFinal"
          language="java"
          since="4.1"
          message="EJB's shouldn't have non-final static fields"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#staticejbfieldshouldbefinal">
        <description>
            According to the J2EE specification, an EJB should not have any static fields
            with write access. However, static read-only fields are allowed. This ensures proper
            behavior especially when instances are distributed by the container on several JREs.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//ClassOrInterfaceDeclaration[
    (
    (./ImplementsList/ClassOrInterfaceType[ends-with(@Image,'SessionBean')])
    or
    (./ImplementsList/ClassOrInterfaceType[ends-with(@Image,'EJBHome')])
    or
    (./ImplementsList/ClassOrInterfaceType[ends-with(@Image,'EJBLocalObject')])
    or
    (./ImplementsList/ClassOrInterfaceType[ends-with(@Image,'EJBLocalHome')])
    or
    (./ExtendsList/ClassOrInterfaceType[ends-with(@Image,'EJBObject')])
    )
    and
    (./ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration[
         (./FieldDeclaration[@Static = 'true'])
         and
         (./FieldDeclaration[@Final = 'false'])
    ])
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class SomeEJB extends EJBObject implements EJBLocalHome {

    private static int CountA;          // poor, field can be edited

    private static final int CountB;    // preferred, read-only access
}
]]>
        </example>
    </rule>

    <rule name="StringBufferInstantiationWithChar"
          language="java"
          since="3.9"
          message="Do not instantiate a StringBuffer or StringBuilder with a char"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#stringbufferinstantiationwithchar">
        <description>
            Individual character values provided as initialization arguments will be converted into integers.
            This can lead to internal buffer sizes that are larger than expected. Some examples:

            ```
            new StringBuffer()      //  16
            new StringBuffer(6)     //  6
            new StringBuffer("hello world")  // 11 + 16 = 27
            new StringBuffer('A')   //  chr(A) = 65
            new StringBuffer("A")   //  1 + 16 = 17

            new StringBuilder()     //  16
            new StringBuilder(6)    //  6
            new StringBuilder("hello world")  // 11 + 16 = 27
            new StringBuilder('C')   //  chr(C) = 67
            new StringBuilder("A")   //  1 + 16 = 17
            ```
        </description>
        <priority>4</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//AllocationExpression/ClassOrInterfaceType
[@Image='StringBuffer' or @Image='StringBuilder']
/../Arguments/ArgumentList/Expression/PrimaryExpression
/PrimaryPrefix/
Literal
  [starts-with(@Image, "'")]
  [ends-with(@Image, "'")]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
// misleading instantiation, these buffers
// are actually sized to 99 characters long
StringBuffer  sb1 = new StringBuffer('c');
StringBuilder sb2 = new StringBuilder('c');

// in these forms, just single characters are allocated
StringBuffer  sb3 = new StringBuffer("c");
StringBuilder sb4 = new StringBuilder("c");
]]>
        </example>
    </rule>

    <rule name="SuspiciousEqualsMethodName"
          language="java"
          since="2.0"
          message="The method name and parameter number are suspiciously close to equals(Object)"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#suspiciousequalsmethodname">
        <description>
            The method name and parameter number are suspiciously close to equals(Object), which can denote an
            intention to override the equals(Object) method.
        </description>
        <priority>2</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//MethodDeclarator[@Image = 'equals']
[
    (count(FormalParameters/*) = 1
    and not (FormalParameters/FormalParameter/Type/ReferenceType/ClassOrInterfaceType
        [@Image = 'Object' or @Image = 'java.lang.Object'])
    or not (../ResultType/Type/PrimitiveType[@Image = 'boolean'])
    )  or  (
    count(FormalParameters/*) = 2
    and ../ResultType/Type/PrimitiveType[@Image = 'boolean']
    and FormalParameters//ClassOrInterfaceType[@Image = 'Object' or @Image = 'java.lang.Object']
    and not(../../Annotation/MarkerAnnotation/Name[@Image='Override'])
    )
]
| //MethodDeclarator[@Image = 'equal']
[
    count(FormalParameters/*) = 1
    and FormalParameters/FormalParameter/Type/ReferenceType/ClassOrInterfaceType
        [@Image = 'Object' or @Image = 'java.lang.Object']
]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
   public int equals(Object o) {
     // oops, this probably was supposed to be boolean equals
   }
   public boolean equals(String s) {
     // oops, this probably was supposed to be equals(Object)
   }
   public boolean equals(Object o1, Object o2) {
     // oops, this probably was supposed to be equals(Object)
   }
}
]]>
        </example>
    </rule>

    <rule name="SuspiciousHashcodeMethodName"
          since="1.5"
          message="The method name and return type are suspiciously close to hashCode()"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.SuspiciousHashcodeMethodNameRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#suspicioushashcodemethodname">
        <description>
            The method name and return type are suspiciously close to hashCode(), which may denote an intention
            to override the hashCode() method.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public class Foo {
    public int hashcode() { // oops, this probably was supposed to be 'hashCode'
    }
}
]]>
        </example>
    </rule>

    <rule name="SuspiciousOctalEscape"
          since="1.5"
          message="Suspicious decimal characters following octal escape in string literal"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.SuspiciousOctalEscapeRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#suspiciousoctalescape">
        <description>
            A suspicious octal escape sequence was found inside a String literal.
            The Java language specification (section 3.10.6) says an octal
            escape sequence inside a literal String shall consist of a backslash
            followed by:

            OctalDigit | OctalDigit OctalDigit | ZeroToThree OctalDigit OctalDigit

            Any octal escape sequence followed by non-octal digits can be confusing,
            e.g. "\038" is interpreted as the octal escape sequence "\03" followed by
            the literal character "8".
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public void foo() {
  // interpreted as octal 12, followed by character '8'
  System.out.println("suspicious: \128");
}
]]>
        </example>
    </rule>

    <rule name="TestClassWithoutTestCases"
          since="3.0"
          message="This class name ends with 'Test' but contains no test cases"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.TestClassWithoutTestCasesRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#testclasswithouttestcases">
        <description>
            Test classes end with the suffix Test. Having a non-test class with that name is not a good practice,
            since most people will assume it is a test case. Test classes have test methods named testXXX.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
//Consider changing the name of the class if it is not a test
//Consider adding test methods if it is a test
public class CarTest {
   public static void main(String[] args) {
    // do something
   }
   // code
}
]]>
        </example>
    </rule>

    <rule name="UnconditionalIfStatement"
          language="java"
          since="1.5"
          message="Do not use 'if' statements that are always true or always false"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unconditionalifstatement">
        <description>
            Do not use "if" statements whose conditionals are always true or always false.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//IfStatement/Expression
 [count(PrimaryExpression)=1]
 /PrimaryExpression/PrimaryPrefix/Literal/BooleanLiteral
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    public void close() {
        if (true) {        // fixed conditional, not recommended
            // ...
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="UnnecessaryBooleanAssertion"
          language="java"
          since="3.0"
          message="assertTrue(true) or similar statements are unnecessary"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          typeResolution="true"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unnecessarybooleanassertion">
        <description>
            A JUnit test assertion with a boolean literal is unnecessary since it always will evaluate to the same thing.
            Consider using flow control (in case of assertTrue(false) or similar) or simply removing
            statements like assertTrue(true) and assertFalse(false).  If you just want a test to halt after finding
            an error, use the fail() method and provide an indication message of why it did.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//StatementExpression
[
PrimaryExpression/PrimaryPrefix/Name[@Image='assertTrue' or  @Image='assertFalse']
and
PrimaryExpression/PrimarySuffix/Arguments/ArgumentList/Expression
[PrimaryExpression/PrimaryPrefix/Literal/BooleanLiteral
or
UnaryExpressionNotPlusMinus[@Image='!']
/PrimaryExpression/PrimaryPrefix[Literal/BooleanLiteral or Name[count(../../*)=1]]]
]
[ancestor::ClassOrInterfaceDeclaration[//ClassOrInterfaceType[pmd-java:typeIs('junit.framework.TestCase')]
    or //MarkerAnnotation/Name[
        pmd-java:typeIs('org.junit.Test')
        or pmd-java:typeIs('org.junit.jupiter.api.Test') or pmd-java:typeIs('org.junit.jupiter.api.RepeatedTest')
        or pmd-java:typeIs('org.junit.jupiter.api.TestFactory') or pmd-java:typeIs('org.junit.jupiter.api.TestTemplate')
        or pmd-java:typeIs('org.junit.jupiter.params.ParameterizedTest')
    ]
]]]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class SimpleTest extends TestCase {
    public void testX() {
        assertTrue(true);       // serves no real purpose
    }
}
]]>
        </example>
    </rule>

    <rule name="UnnecessaryCaseChange"
          since="3.3"
          message="Using equalsIgnoreCase() is cleaner than using toUpperCase/toLowerCase().equals()."
          class="net.sourceforge.pmd.lang.java.rule.errorprone.UnnecessaryCaseChangeRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unnecessarycasechange">
        <description>
            Using equalsIgnoreCase() is faster than using toUpperCase/toLowerCase().equals()
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
boolean answer1 = buz.toUpperCase().equals("baz");              // should be buz.equalsIgnoreCase("baz")

boolean answer2 = buz.toUpperCase().equalsIgnoreCase("baz");    // another unnecessary toUpperCase()
]]>
        </example>
    </rule>

    <rule name="UnnecessaryConversionTemporary"
          since="0.1"
          message="Avoid unnecessary temporaries when converting primitives to Strings"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.UnnecessaryConversionTemporaryRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unnecessaryconversiontemporary">
        <description>
            Avoid the use temporary objects when converting primitives to Strings. Use the static conversion methods
            on the wrapper classes instead.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
public String convert(int x) {
    String foo = new Integer(x).toString(); // this wastes an object

    return Integer.toString(x);             // preferred approach
}
]]>
        </example>
    </rule>

    <rule name="UnusedNullCheckInEquals"
          language="java"
          since="3.5"
          message="Invoke equals() on the object you''ve already ensured is not null"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#unusednullcheckinequals">
        <description>
            After checking an object reference for null, you should invoke equals() on that object rather than passing it to another object's equals() method.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
(//PrimaryPrefix[ends-with(Name/@Image, '.equals') and Name/@Image != 'Arrays.equals'] | //PrimarySuffix[@Image='equals' and not(../PrimaryPrefix/Literal)])
 /following-sibling::PrimarySuffix/Arguments/ArgumentList/Expression
 /PrimaryExpression[count(PrimarySuffix)=0]/PrimaryPrefix
 /Name[@Image = ./../../../../../../../../../../Expression/ConditionalAndExpression
 /EqualityExpression[@Image="!=" and count(./preceding-sibling::*)=0 and
 ./PrimaryExpression/PrimaryPrefix/Literal/NullLiteral]
  /PrimaryExpression/PrimaryPrefix/Name/@Image]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Test {

    public String method1() { return "ok";}
    public String method2() { return null;}

    public void method(String a) {
        String b;
        // I don't know it method1() can be "null"
        // but I know "a" is not null..
        // I'd better write a.equals(method1())

        if (a!=null && method1().equals(a)) { // will trigger the rule
            //whatever
        }

        if (method1().equals(a) && a != null) { // won't trigger the rule
            //whatever
        }

        if (a!=null && method1().equals(b)) { // won't trigger the rule
            //whatever
        }

        if (a!=null && "LITERAL".equals(a)) { // won't trigger the rule
            //whatever
        }

        if (a!=null && !a.equals("go")) { // won't trigger the rule
            a=method2();
            if (method1().equals(a)) {
                //whatever
            }
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="UseCorrectExceptionLogging"
          language="java"
          since="3.2"
          message="Use the correct logging statement for logging exceptions"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#usecorrectexceptionlogging">
        <description>
            To make sure the full stacktrace is printed out, use the logging statement with two arguments: a String and a Throwable.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//CatchStatement/Block/BlockStatement/Statement/StatementExpression
/PrimaryExpression[PrimaryPrefix/Name[starts-with(@Image,
concat(ancestor::ClassOrInterfaceDeclaration/ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/FieldDeclaration
[Type//ClassOrInterfaceType[@Image='Log']]
/VariableDeclarator/VariableDeclaratorId/@Image, '.'))]]
[PrimarySuffix/Arguments[@ArgumentCount='1']]
[PrimarySuffix/Arguments//Name/@Image = ancestor::CatchStatement/FormalParameter/VariableDeclaratorId/@Image]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Main {
    private static final Log _LOG = LogFactory.getLog( Main.class );
    void bar() {
        try {
        } catch( Exception e ) {
            _LOG.error( e ); //Wrong!
        } catch( OtherException oe ) {
            _LOG.error( oe.getMessage(), oe ); //Correct
        }
    }
}
]]>
        </example>
    </rule>

    <rule name="UseEqualsToCompareStrings"
          language="java"
          since="4.1"
          message="Use equals() to compare strings instead of ''=='' or ''!=''"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#useequalstocomparestrings">
        <description>
            Using '==' or '!=' to compare strings only works if intern version is used on both sides.
            Use the equals() method instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//EqualityExpression/PrimaryExpression
[(PrimaryPrefix/Literal
   [starts-with(@Image, '"')]
   [ends-with(@Image, '"')]
and count(PrimarySuffix) = 0)]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
public boolean test(String s) {
    if (s == "one") return true;        // unreliable
    if ("two".equals(s)) return true;   // better
    return false;
}
]]>
        </example>
    </rule>

    <rule name="UselessOperationOnImmutable"
          since="3.5"
          message="An operation on an Immutable object (String, BigDecimal or BigInteger) won't change the object itself"
          class="net.sourceforge.pmd.lang.java.rule.errorprone.UselessOperationOnImmutableRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#uselessoperationonimmutable">
        <description>
            An operation on an Immutable object (String, BigDecimal or BigInteger) won't change the object itself
            since the result of the operation is a new object. Therefore, ignoring the operation result is an error.
        </description>
        <priority>3</priority>
        <example>
            <![CDATA[
import java.math.*;

class Test {
    void method1() {
        BigDecimal bd=new BigDecimal(10);
        bd.add(new BigDecimal(5));      // this will trigger the rule
    }
    void method2() {
        BigDecimal bd=new BigDecimal(10);
        bd = bd.add(new BigDecimal(5)); // this won't trigger the rule
    }
}
]]>
        </example>
    </rule>

    <rule name="UseLocaleWithCaseConversions"
          language="java"
          since="2.0"
          message="When doing a String.toLowerCase()/toUpperCase() call, use a Locale"
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#uselocalewithcaseconversions">
        <description>
            When doing String.toLowerCase()/toUpperCase() conversions, use Locales to avoids problems with languages that
            have unusual conventions, i.e. Turkish.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>
                    <![CDATA[
//PrimaryExpression
[
PrimaryPrefix
[Name[ends-with(@Image, 'toLowerCase') or ends-with(@Image, 'toUpperCase')]]
[following-sibling::PrimarySuffix[position() = 1]/Arguments[@ArgumentCount=0]]

or

PrimarySuffix
[ends-with(@Image, 'toLowerCase') or ends-with(@Image, 'toUpperCase')]
[following-sibling::PrimarySuffix[position() = 1]/Arguments[@ArgumentCount=0]]
]
[not(PrimaryPrefix/Name[ends-with(@Image, 'toHexString')])]
]]>
                </value>
            </property>
        </properties>
        <example>
            <![CDATA[
class Foo {
    // BAD
    if (x.toLowerCase().equals("list")) { }

    /*
     * This will not match "LIST" when in Turkish locale
     * The above could be
     * if (x.toLowerCase(Locale.US).equals("list")) { }
     * or simply
     * if (x.equalsIgnoreCase("list")) { }
     */
    // GOOD
    String z = a.toLowerCase(Locale.EN);
}
]]>
        </example>
    </rule>

    <rule name="UseProperClassLoader"
          language="java"
          since="3.7"
          message="In J2EE, getClassLoader() might not work as expected.  Use Thread.currentThread().getContextClassLoader() instead."
          class="net.sourceforge.pmd.lang.rule.XPathRule"
          externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#useproperclassloader">
        <description>
            In J2EE, the getClassLoader() method might not work as expected. Use
            Thread.currentThread().getContextClassLoader() instead.
        </description>
        <priority>3</priority>
        <properties>
            <property name="xpath">
                <value>//PrimarySuffix[@Image='getClassLoader']</value>
            </property>
        </properties>
        <example>
            <![CDATA[
public class Foo {
    ClassLoader cl = Bar.class.getClassLoader();
}
]]>
        </example>
    </rule>

</ruleset>