Code Style

AbstractNaming

Deprecated

Since: PMD 1.4

Priority: Medium (3)

Abstract classes should be named ‘AbstractXXX’.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration
 [@Abstract='true' and @Interface='false']
 [not (starts-with(@Image,'Abstract'))]
|
//ClassOrInterfaceDeclaration
 [@Abstract='false']
 [$strict='true']
 [starts-with(@Image, 'Abstract')]

Example(s):

public abstract class Foo { // should be AbstractFoo
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/AbstractNaming" />

AtLeastOneConstructor

Since: PMD 1.04

Priority: Medium (3)

Each class should declare at least one constructor.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[
  not(ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/ConstructorDeclaration)
  and
  (@Static = 'false')
  and
  (count(./descendant::MethodDeclaration[@Static = 'true']) < 1)
]
  [@Interface='false']

Example(s):

public class Foo {
   // missing constructor
  public void doSomething() { ... }
  public void doOtherThing { ... }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/AtLeastOneConstructor" />

AvoidDollarSigns

Since: PMD 1.5

Priority: Medium (3)

Avoid using dollar signs in variable/method/class/interface names.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.AvoidDollarSignsRule

Example(s):

public class Fo$o {  // not a recommended name
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/AvoidDollarSigns" />

AvoidFinalLocalVariable

Since: PMD 4.1

Priority: Medium (3)

Avoid using final local variables, turn them into fields.

This rule is defined by the following XPath expression:

//LocalVariableDeclaration[
  @Final = 'true'
  and not(../../ForStatement)
  and
  (
    (count(VariableDeclarator/VariableInitializer) = 0)
    or
    (VariableDeclarator/VariableInitializer/Expression/PrimaryExpression/PrimaryPrefix/Literal)
  )
]

Example(s):

public class MyClass {
    public void foo() {
        final String finalLocalVariable;
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/AvoidFinalLocalVariable" />

AvoidPrefixingMethodParameters

Since: PMD 5.0

Priority: Medium Low (4)

Prefixing parameters by ‘in’ or ‘out’ pollutes the name of the parameters and reduces code readability. To indicate whether or not a parameter will be modify in a method, its better to document method behavior with Javadoc.

This rule is defined by the following XPath expression:

//MethodDeclaration/MethodDeclarator/FormalParameters/FormalParameter/VariableDeclaratorId[
        pmd:matches(@Image,'^in[A-Z].*','^out[A-Z].*','^in$','^out$')
]

Example(s):

// Not really clear
public class Foo {
  public void bar(
      int inLeftOperand,
      Result outRightOperand) {
      outRightOperand.setValue(inLeftOperand * outRightOperand.getValue());
  }
}

// Far more useful
public class Foo {
  /**
   *
   * @param leftOperand, (purpose), not modified by method.
   * @param rightOperand (purpose), will be modified by the method: contains the result.
   */
  public void bar(
        int leftOperand,
        Result rightOperand) {
        rightOperand.setValue(leftOperand * rightOperand.getValue());
  }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/AvoidPrefixingMethodParameters" />

AvoidProtectedFieldInFinalClass

Since: PMD 2.1

Priority: Medium (3)

Do not use protected fields in final classes since they cannot be subclassed. Clarify your intent by using private or package access modifiers instead.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[@Final='true']
/ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration
/FieldDeclaration[@Protected='true']

Example(s):

public final class Bar {
  private int x;
  protected int y;  // bar cannot be subclassed, so is y really private or package visible?
  Bar() {}
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/AvoidProtectedFieldInFinalClass" />

AvoidProtectedMethodInFinalClassNotExtending

Since: PMD 5.1

Priority: Medium (3)

Do not use protected methods in most final classes since they cannot be subclassed. This should only be allowed in final classes that extend other classes with protected methods (whose visibility cannot be reduced). Clarify your intent by using private or package access modifiers instead.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[@Final='true' and not(ExtendsList)]
/ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration
/MethodDeclaration[@Protected='true'][MethodDeclarator/@Image != 'finalize']

Example(s):

public final class Foo {
  private int bar() {}
  protected int baz() {} // Foo cannot be subclassed, and doesn't extend anything, so is baz() really private or package visible?
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/AvoidProtectedMethodInFinalClassNotExtending" />

AvoidUsingNativeCode

Since: PMD 4.1

Priority: Medium High (2)

Unnecessary reliance on Java Native Interface (JNI) calls directly reduces application portability and increases the maintenance burden.

This rule is defined by the following XPath expression:

//Name[starts-with(@Image,'System.loadLibrary')]

Example(s):

public class SomeJNIClass {

     public SomeJNIClass() {
         System.loadLibrary("nativelib");
     }

     static {
         System.loadLibrary("nativelib");
     }

     public void invalidCallsInMethod() throws SecurityException, NoSuchMethodException {
         System.loadLibrary("nativelib");
     }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/AvoidUsingNativeCode" />

BooleanGetMethodName

Since: PMD 4.0

Priority: Medium Low (4)

Methods that return boolean results should be named as predicate statements to denote this. I.e, ‘isReady()’, ‘hasValues()’, ‘canCommit()’, ‘willFail()’, etc. Avoid the use of the ‘get’ prefix for these methods.

This rule is defined by the following XPath expression:

//MethodDeclaration[
MethodDeclarator[count(FormalParameters/FormalParameter) = 0 or $checkParameterizedMethods = 'true']
                [starts-with(@Image, 'get')]
and
ResultType/Type/PrimitiveType[@Image = 'boolean']
and not(../Annotation//Name[@Image = 'Override'])
]

Example(s):

public boolean getFoo();            // bad
public boolean isFoo();             // ok
public boolean getFoo(boolean bar); // ok, unless checkParameterizedMethods=true

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/BooleanGetMethodName" />

CallSuperInConstructor

Since: PMD 3.0

Priority: Medium (3)

It is a good practice to call super() in a constructor. If super() is not called but another constructor (such as an overloaded constructor) is called, this rule will not report it.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[ count (ExtendsList/*) > 0 ]
/ClassOrInterfaceBody
 /ClassOrInterfaceBodyDeclaration
 /ConstructorDeclaration[ count (.//ExplicitConstructorInvocation)=0 ]

Example(s):

public class Foo extends Bar{
  public Foo() {
   // call the constructor of Bar
   super();
  }
 public Foo(int code) {
  // do something with code
   this();
   // no problem with this
  }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/CallSuperInConstructor" />

ClassNamingConventions

Since: PMD 1.2

Priority: High (1)

Configurable naming conventions for type declarations. This rule reports type declarations which do not match the regex that applies to their specific kind (e.g. enum or interface). Each regex can be configured through properties.

By default this rule uses the standard Java naming convention (Pascal case), and reports utility class names not ending with ‘Util’.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.ClassNamingConventionsRule

Example(s):

// This is Pascal case, the recommended naming convention in Java
// Note that the default values of this rule don't allow numbers,
// underscores, or accented characters in type names
public class FooBar {}

// You may want abstract classes to be named 'AbstractXXX',
// in which case you can customize the regex for abstract
// classes to 'Abstract[A-Z]\w+'
public abstract class Thing {}

// This class doesn't respect the convention, and will be flagged
public class Éléphant {}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ClassNamingConventions" />

CommentDefaultAccessModifier

Since: PMD 5.4.0

Priority: Medium (3)

To avoid mistakes if we want that a Method, Constructor, Field or Nested class have a default access modifier we must add a comment at the beginning of it’s declaration. By default the comment must be /* default */, if you want another, you have to provide a regexp.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.CommentDefaultAccessModifierRule

Example(s):

public class Foo {
    final String stringValue = "some string";
    String getString() {
       return stringValue;
    }

    class NestedFoo {
    }
}

// should be
public class Foo {
    /* default */ final String stringValue = "some string";
    /* default */ String getString() {
       return stringValue;
    }

    /* default */ class NestedFoo {
    }
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/CommentDefaultAccessModifier" />

ConfusingTernary

Since: PMD 1.9

Priority: Medium (3)

Avoid negation within an “if” expression with an “else” clause. For example, rephrase: if (x != y) diff(); else same(); as: if (x == y) same(); else diff();.

Most “if (x != y)” cases without an “else” are often return cases, so consistent use of this rule makes the code easier to read. Also, this resolves trivial ordering problems, such as “does the error case go first?” or “does the common case go first?”.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.ConfusingTernaryRule

Example(s):

boolean bar(int x, int y) {
    return (x != y) ? diff : same;
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ConfusingTernary" />

ControlStatementBraces

Since: PMD 6.2.0

Priority: Medium (3)

Enforce a policy for braces on control statements. It is recommended to use braces on ‘if … else’ statements and loop statements, even if they are optional. This usually makes the code clearer, and helps prepare the future when you need to add another statement. That said, this rule lets you control which statements are required to have braces via properties.

From 6.2.0 on, this rule supersedes WhileLoopMustUseBraces, ForLoopMustUseBraces, IfStmtMustUseBraces, and IfElseStmtMustUseBraces.

This rule is defined by the following XPath expression:

//WhileStatement[$checkWhileStmt and not(Statement/Block) and not($allowEmptyLoop and Statement/EmptyStatement)]
                |
                //ForStatement[$checkForStmt and not(Statement/Block) and not($allowEmptyLoop and Statement/EmptyStatement)]
                |
                //DoStatement[$checkDoWhileStmt and not(Statement/Block) and not($allowEmptyLoop and Statement/EmptyStatement)]
                |
                (: The violation is reported on the sub statement -- not the if statement :)
                //Statement[$checkIfElseStmt and parent::IfStatement and not(child::Block or child::IfStatement)
                            (: Whitelists single if statements :)
                            and ($checkSingleIfStmt
                                 (: Inside this not(...) is the definition of a "single if statement" :)
                                 or not(count(../Statement) = 1 (: No else stmt :)
                                        (: Not the last branch of an 'if ... else if' chain :)
                                        and not(parent::IfStatement[parent::Statement[parent::IfStatement]])))]
                |
                (: Reports case labels if one of their subordinate statements is not braced :)
                //SwitchLabel[$checkCaseStmt]
                             [count(following-sibling::BlockStatement except following-sibling::SwitchLabel[1]/following-sibling::BlockStatement) > 1
                              or (some $stmt (: in only the block statements until the next label :)
                                  in following-sibling::BlockStatement except following-sibling::SwitchLabel[1]/following-sibling::BlockStatement
                                  satisfies not($stmt/Statement/Block))]

Example(s):

while (true)    // not recommended
  x++;

while (true) {  // preferred approach
  x++;
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ControlStatementBraces" />

DefaultPackage

Since: PMD 3.4

Priority: Medium (3)

Use explicit scoping instead of accidental usage of default package private level. The rule allows methods and fields annotated with Guava’s @VisibleForTesting.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[@Interface='false']
/ClassOrInterfaceBody
/ClassOrInterfaceBodyDeclaration
[not(Annotation//Name[ends-with(@Image, 'VisibleForTesting')])]
[
FieldDeclaration[@PackagePrivate='true']
or MethodDeclaration[@PackagePrivate='true']
]

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/DefaultPackage" />

DontImportJavaLang

Since: PMD 0.5

Priority: Medium Low (4)

Avoid importing anything from the package ‘java.lang’. These classes are automatically imported (JLS 7.5.3).

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.DontImportJavaLangRule

Example(s):

import java.lang.String;    // this is unnecessary

public class Foo {}

// --- in another source code file...

import java.lang.*;         // this is bad

public class Foo {}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/DontImportJavaLang" />

DuplicateImports

Since: PMD 0.5

Priority: Medium Low (4)

Duplicate or overlapping import statements should be avoided.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.DuplicateImportsRule

Example(s):

import java.lang.String;
import java.lang.*;
public class Foo {}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/DuplicateImports" />

EmptyMethodInAbstractClassShouldBeAbstract

Since: PMD 4.1

Priority: High (1)

Empty or auto-generated methods in an abstract class should be tagged as abstract. This helps to remove their inapproprate usage by developers who should be implementing their own versions in the concrete subclasses.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[@Abstract = 'true']
    /ClassOrInterfaceBody
    /ClassOrInterfaceBodyDeclaration
    /MethodDeclaration[@Abstract = 'false' and @Native = 'false']
    [
        ( boolean(./Block[count(./BlockStatement) =  1]/BlockStatement/Statement/ReturnStatement/Expression/PrimaryExpression/PrimaryPrefix/Literal/NullLiteral) = 'true' )
        or
        ( boolean(./Block[count(./BlockStatement) =  1]/BlockStatement/Statement/ReturnStatement/Expression/PrimaryExpression/PrimaryPrefix/Literal[@Image = '0']) = 'true' )
        or
        ( boolean(./Block[count(./BlockStatement) =  1]/BlockStatement/Statement/ReturnStatement/Expression/PrimaryExpression/PrimaryPrefix/Literal[string-length(@Image) = 2]) = 'true' )
        or
        (./Block[count(./BlockStatement) =  1]/BlockStatement/Statement/EmptyStatement)
        or
        ( count (./Block/*) = 0 )
    ]

Example(s):

public abstract class ShouldBeAbstract {
    public Object couldBeAbstract() {
        // Should be abstract method ?
        return null;
    }

    public void couldBeAbstract() {
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/EmptyMethodInAbstractClassShouldBeAbstract" />

ExtendsObject

Since: PMD 5.0

Priority: Medium Low (4)

No need to explicitly extend Object.

This rule is defined by the following XPath expression:

//ExtendsList/ClassOrInterfaceType[@Image='Object' or @Image='java.lang.Object']

Example(s):

public class Foo extends Object {     // not required
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ExtendsObject" />

FieldDeclarationsShouldBeAtStartOfClass

Since: PMD 5.0

Priority: Medium (3)

Fields should be declared at the top of the class, before any method declarations, constructors, initializers or inner classes.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.FieldDeclarationsShouldBeAtStartOfClassRule

Example(s):

public class HelloWorldBean {

  // Field declared before methods / inner classes - OK
  private String _thing;

  public String getMessage() {
    return "Hello World!";
  }

  // Field declared after methods / inner classes - avoid this
  private String _fieldInWrongLocation;
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/FieldDeclarationsShouldBeAtStartOfClass" />

ForLoopShouldBeWhileLoop

Since: PMD 1.02

Priority: Medium (3)

Some for loops can be simplified to while loops, this makes them more concise.

This rule is defined by the following XPath expression:

//ForStatement
  [not(LocalVariableDeclaration)]
  [not(ForInit)]
  [not(ForUpdate)]
  [Expression]

Example(s):

public class Foo {
    void bar() {
        for (;true;) true; // No Init or Update part, may as well be: while (true)
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ForLoopShouldBeWhileLoop" />

ForLoopsMustUseBraces

Deprecated

Since: PMD 0.7

Priority: Medium (3)

Avoid using ‘for’ statements without using curly braces. If the code formatting or indentation is lost then it becomes difficult to separate the code being controlled from the rest.

This rule is defined by the following XPath expression:

//ForStatement[not(Statement/Block)]

Example(s):

for (int i = 0; i < 42; i++)
   foo();

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ForLoopsMustUseBraces" />

GenericsNaming

Since: PMD 4.2.6

Priority: Medium Low (4)

Names for references to generic values should be limited to a single uppercase letter.

This rule is defined by the following XPath expression:

//TypeDeclaration/ClassOrInterfaceDeclaration/TypeParameters/TypeParameter[
  string-length(@Image) > 1 
  or
  string:upper-case(@Image) != @Image
]

Example(s):

public interface GenericDao<E extends BaseModel, K extends Serializable> extends BaseDao {
    // This is ok...
}

public interface GenericDao<E extends BaseModel, K extends Serializable> {
    // Also this
}

public interface GenericDao<e extends BaseModel, K extends Serializable> {
    // 'e' should be an 'E'
}

public interface GenericDao<EF extends BaseModel, K extends Serializable> {
   // 'EF' is not ok.
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/GenericsNaming" />

IfElseStmtsMustUseBraces

Deprecated

Since: PMD 0.2

Priority: Medium (3)

Avoid using if..else statements without using surrounding braces. If the code formatting or indentation is lost then it becomes difficult to separate the code being controlled from the rest.

This rule is defined by the following XPath expression:

//Statement
 [parent::IfStatement[@Else='true']]
 [not(child::Block)]
 [not(child::IfStatement)]

Example(s):

// this is OK
if (foo) x++;

   // but this is not
if (foo)
       x = x+1;
   else
       x = x-1;

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/IfElseStmtsMustUseBraces" />

IfStmtsMustUseBraces

Deprecated

Since: PMD 1.0

Priority: Medium (3)

Avoid using if statements without using braces to surround the code block. If the code formatting or indentation is lost then it becomes difficult to separate the code being controlled from the rest.

This rule is defined by the following XPath expression:

//IfStatement[count(*) < 3][not(Statement/Block)]

Example(s):

if (foo)    // not recommended
    x++;

if (foo) {  // preferred approach
    x++;
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/IfStmtsMustUseBraces" />

LocalHomeNamingConvention

Since: PMD 4.0

Priority: Medium Low (4)

The Local Home interface of a Session EJB should be suffixed by ‘LocalHome’.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration
[
    (
        (./ExtendsList/ClassOrInterfaceType[ends-with(@Image,'EJBLocalHome')])
    )
    and
    not
    (
        ends-with(@Image,'LocalHome')
    )
]

Example(s):

public interface MyBeautifulLocalHome extends javax.ejb.EJBLocalHome {} // proper name

public interface MissingProperSuffix extends javax.ejb.EJBLocalHome {}  // non-standard name

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/LocalHomeNamingConvention" />

LocalInterfaceSessionNamingConvention

Since: PMD 4.0

Priority: Medium Low (4)

The Local Interface of a Session EJB should be suffixed by ‘Local’.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration
[
    (
        (./ExtendsList/ClassOrInterfaceType[ends-with(@Image,'EJBLocalObject')])
    )
    and
    not
    (
        ends-with(@Image,'Local')
    )
]

Example(s):

public interface MyLocal extends javax.ejb.EJBLocalObject {}                // proper name

public interface MissingProperSuffix extends javax.ejb.EJBLocalObject {}    // non-standard name

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/LocalInterfaceSessionNamingConvention" />

LocalVariableCouldBeFinal

Since: PMD 2.2

Priority: Medium (3)

A local variable assigned only once can be declared final.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.LocalVariableCouldBeFinalRule

Example(s):

public class Bar {
    public void foo () {
    String txtA = "a";          // if txtA will not be assigned again it is better to do this:
    final String txtB = "b";
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/LocalVariableCouldBeFinal" />

LongVariable

Since: PMD 0.3

Priority: Medium (3)

Fields, formal arguments, or local variable names that are too long can make the code difficult to follow.

This rule is defined by the following XPath expression:

//VariableDeclaratorId[string-length(@Image) > $minimum]

Example(s):

public class Something {
    int reallyLongIntName = -3;             // VIOLATION - Field
    public static void main( String argumentsList[] ) { // VIOLATION - Formal
        int otherReallyLongName = -5;       // VIOLATION - Local
        for (int interestingIntIndex = 0;   // VIOLATION - For
             interestingIntIndex < 10;
             interestingIntIndex ++ ) {
    }
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/LongVariable" />

MDBAndSessionBeanNamingConvention

Since: PMD 4.0

Priority: Medium Low (4)

The EJB Specification states that any MessageDrivenBean or SessionBean should be suffixed by ‘Bean’.

This rule is defined by the following XPath expression:

//TypeDeclaration/ClassOrInterfaceDeclaration
[
    (
        (./ImplementsList/ClassOrInterfaceType[ends-with(@Image,'SessionBean')])
        or
        (./ImplementsList/ClassOrInterfaceType[ends-with(@Image,'MessageDrivenBean')])
    )
    and
    not
    (
        ends-with(@Image,'Bean')
    )
]

Example(s):

public class SomeBean implements SessionBean{}                  // proper name

public class MissingTheProperSuffix implements SessionBean {}   // non-standard name

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/MDBAndSessionBeanNamingConvention" />

MethodArgumentCouldBeFinal

Since: PMD 2.2

Priority: Medium (3)

A method argument that is never re-assigned within the method can be declared final.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.MethodArgumentCouldBeFinalRule

Example(s):

public void foo1 (String param) {       // do stuff with param never assigning it

}

public void foo2 (final String param) { // better, do stuff with param never assigning it

}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/MethodArgumentCouldBeFinal" />

MethodNamingConventions

Since: PMD 1.2

Priority: High (1)

Configurable naming conventions for method declarations. This rule reports method declarations which do not match the regex that applies to their specific kind (e.g. JUnit test or native method). Each regex can be configured through properties.

By default this rule uses the standard Java naming convention (Camel case).

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.MethodNamingConventionsRule

Example(s):

public class Foo {
    public void fooStuff() {
    }
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/MethodNamingConventions" />

MIsLeadingVariableName

Since: PMD 3.4

Priority: Medium (3)

Detects when a non-field has a name starting with ‘m_’. This usually denotes a field and could be confusing.

This rule is defined by the following XPath expression:

//VariableDeclaratorId
[starts-with(@Image, 'm_')]
[not (../../../FieldDeclaration)]

Example(s):

public class Foo {
    private int m_foo; // OK
    public void bar(String m_baz) { // Bad
      int m_boz = 42; // Bad
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/MIsLeadingVariableName" />

NoPackage

Since: PMD 3.3

Priority: Medium (3)

Detects when a class or interface does not have a package definition.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[count(preceding::PackageDeclaration) = 0]

Example(s):

// no package declaration
public class ClassInDefaultPackage {
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/NoPackage" />

OnlyOneReturn

Since: PMD 1.0

Priority: Medium (3)

A method should have only one exit point, and that should be the last statement in the method.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.OnlyOneReturnRule

Example(s):

public class OneReturnOnly1 {
  public void foo(int x) {
    if (x > 0) {
      return "hey";   // first exit
    }
    return "hi";    // second exit
  }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/OnlyOneReturn" />

PackageCase

Since: PMD 3.3

Priority: Medium (3)

Detects when a package definition contains uppercase characters.

This rule is defined by the following XPath expression:

//PackageDeclaration/Name[lower-case(@Image)!=@Image]

Example(s):

package com.MyCompany;  // should be lowercase name

public class SomeClass {
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/PackageCase" />

PrematureDeclaration

Since: PMD 5.0

Priority: Medium (3)

Checks for variables that are defined before they might be used. A reference is deemed to be premature if it is created right before a block of code that doesn’t use it that also has the ability to return or throw an exception.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.PrematureDeclarationRule

Example(s):

public int getLength(String[] strings) {

    int length = 0; // declared prematurely

    if (strings == null || strings.length == 0) return 0;

    for (String str : strings) {
        length += str.length();
    }

    return length;
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/PrematureDeclaration" />

RemoteInterfaceNamingConvention

Since: PMD 4.0

Priority: Medium Low (4)

Remote Interface of a Session EJB should not have a suffix.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration
[
    (
        (./ExtendsList/ClassOrInterfaceType[ends-with(@Image,'EJBObject')])
    )
    and
    (
        ends-with(@Image,'Session')
        or
        ends-with(@Image,'EJB')
        or
        ends-with(@Image,'Bean')
    )
]

Example(s):

/* Poor Session suffix */
public interface BadSuffixSession extends javax.ejb.EJBObject {}

/* Poor EJB suffix */
public interface BadSuffixEJB extends javax.ejb.EJBObject {}

/* Poor Bean suffix */
public interface BadSuffixBean extends javax.ejb.EJBObject {}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/RemoteInterfaceNamingConvention" />

RemoteSessionInterfaceNamingConvention

Since: PMD 4.0

Priority: Medium Low (4)

A Remote Home interface type of a Session EJB should be suffixed by ‘Home’.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration
[
    (
        (./ExtendsList/ClassOrInterfaceType[ends-with(@Image,'EJBHome')])
    )
    and
    not
    (
        ends-with(@Image,'Home')
    )
]

Example(s):

public interface MyBeautifulHome extends javax.ejb.EJBHome {}       // proper name

public interface MissingProperSuffix extends javax.ejb.EJBHome {}   // non-standard name

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/RemoteSessionInterfaceNamingConvention" />

ShortClassName

Since: PMD 5.0

Priority: Medium Low (4)

Short Classnames with fewer than e.g. five characters are not recommended.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[string-length(@Image) < $minimum]

Example(s):

public class Foo {
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ShortClassName" />

ShortMethodName

Since: PMD 0.3

Priority: Medium (3)

Method names that are very short are not helpful to the reader.

This rule is defined by the following XPath expression:

//MethodDeclarator[string-length(@Image) < $minimum]

Example(s):

public class ShortMethod {
    public void a( int i ) { // Violation
    }
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ShortMethodName" />

ShortVariable

Since: PMD 0.3

Priority: Medium (3)

Fields, local variables, or parameter names that are very short are not helpful to the reader.

This rule is defined by the following XPath expression:

//VariableDeclaratorId[string-length(@Image) < $minimum]
 [not(ancestor::ForInit)]
 [not(../../VariableDeclarator and ../../../LocalVariableDeclaration and ../../../../ForStatement)]
 [not((ancestor::FormalParameter) and (ancestor::TryStatement))]

Example(s):

public class Something {
    private int q = 15;                         // field - too short
    public static void main( String as[] ) {    // formal arg - too short
        int r = 20 + q;                         // local var - too short
        for (int i = 0; i < 10; i++) {          // not a violation (inside 'for' loop)
            r += q;
        }
        for (Integer i : numbers) {             // not a violation (inside 'for-each' loop)
            r += q;
        }
    }
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/ShortVariable" />

SuspiciousConstantFieldName

Since: PMD 2.0

Priority: Medium (3)

Field names using all uppercase characters - Sun’s Java naming conventions indicating constants - should be declared as final.

This rule is defined by the following XPath expression:

//ClassOrInterfaceDeclaration[@Interface='false']
 /ClassOrInterfaceBody/ClassOrInterfaceBodyDeclaration/FieldDeclaration
  [@Final='false']
  [VariableDeclarator/VariableDeclaratorId[upper-case(@Image)=@Image]]

Example(s):

public class Foo {
 // this is bad, since someone could accidentally
 // do PI = 2.71828; which is actually e
 // final double PI = 3.16; is ok
  double PI = 3.16;
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/SuspiciousConstantFieldName" />

TooManyStaticImports

Since: PMD 4.1

Priority: Medium (3)

If you overuse the static import feature, it can make your program unreadable and unmaintainable, polluting its namespace with all the static members you import. Readers of your code (including you, a few months after you wrote it) will not know which class a static member comes from (Sun 1.5 Language Guide).

This rule is defined by the following XPath expression:

.[count(ImportDeclaration[@Static = 'true']) > $maximumStaticImports]

Example(s):

import static Lennon;
import static Ringo;
import static George;
import static Paul;
import static Yoko; // Too much !

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/TooManyStaticImports" />

UnnecessaryAnnotationValueElement

Since: PMD 6.2.0

Priority: Medium (3)

Avoid the use of value in annotations when it’s the only element.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryAnnotationValueElementRule

Example(s):

@TestClassAnnotation(value = "TEST")
public class Foo {

    @TestMemberAnnotation(value = "TEST")
    private String y;

    @TestMethodAnnotation(value = "TEST")
    public void bar() {
        int x = 42;
        return;
    }
}

// should be

@TestClassAnnotation("TEST")
public class Foo {

    @TestMemberAnnotation("TEST")
    private String y;

    @TestMethodAnnotation("TEST")
    public void bar() {
        int x = 42;
        return;
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/UnnecessaryAnnotationValueElement" />

UnnecessaryConstructor

Since: PMD 1.0

Priority: Medium (3)

This rule detects when a constructor is not necessary; i.e., when there is only one constructor and the constructor is identical to the default constructor. The default constructor should has same access modifier as the declaring class. In an enum type, the default constructor is implicitly private.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryConstructorRule

Example(s):

public class Foo {
  public Foo() {}
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/UnnecessaryConstructor" />

UnnecessaryFullyQualifiedName

Since: PMD 5.0

Priority: Medium Low (4)

Import statements allow the use of non-fully qualified names. The use of a fully qualified name which is covered by an import statement is redundant. Consider using the non-fully qualified name.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryFullyQualifiedNameRule

Example(s):

import java.util.List;

public class Foo {
    private java.util.List list1;   // Unnecessary FQN
    private List list2;             // More appropriate given import of 'java.util.List'
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/UnnecessaryFullyQualifiedName" />

UnnecessaryLocalBeforeReturn

Since: PMD 3.3

Priority: Medium (3)

Avoid the creation of unnecessary local variables

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryLocalBeforeReturnRule

Example(s):

public class Foo {
   public int foo() {
     int x = doSomething();
     return x;  // instead, just 'return doSomething();'
   }
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/UnnecessaryLocalBeforeReturn" />

UnnecessaryModifier

Since: PMD 1.02

Priority: Medium (3)

Fields in interfaces and annotations are automatically public static final, and methods are public abstract. Classes, interfaces or annotations nested in an interface or annotation are automatically public static (all nested interfaces and annotations are automatically static). Nested enums are automatically static. For historical reasons, modifiers which are implied by the context are accepted by the compiler, but are superfluous.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryModifierRule

Example(s):

public @interface Annotation {
    public abstract void bar();     // both abstract and public are ignored by the compiler
    public static final int X = 0;  // public, static, and final all ignored
    public static class Bar {}      // public, static ignored
    public static interface Baz {}  // ditto
}
public interface Foo {
    public abstract void bar();     // both abstract and public are ignored by the compiler
    public static final int X = 0;  // public, static, and final all ignored
    public static class Bar {}      // public, static ignored
    public static interface Baz {}  // ditto
}
public class Bar {
    public static interface Baz {}  // static ignored
    public static enum FoorBar {    // static ignored
        FOO;
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/UnnecessaryModifier" />

UnnecessaryReturn

Since: PMD 1.3

Priority: Medium (3)

Avoid the use of unnecessary return statements.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.UnnecessaryReturnRule

Example(s):

public class Foo {
    public void bar() {
        int x = 42;
        return;
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/UnnecessaryReturn" />

UselessParentheses

Since: PMD 5.0

Priority: Medium Low (4)

Useless parentheses should be removed.

This rule is defined by the following XPath expression:

//Expression[not(parent::PrimaryPrefix)]/PrimaryExpression[count(*)>1]
  /PrimaryPrefix/Expression
    [not(./CastExpression)]
    [not(./ConditionalExpression[@Ternary='true'])]
    [not(./AdditiveExpression)]
|
//Expression[not(parent::PrimaryPrefix)]/PrimaryExpression[count(*)=1]
  /PrimaryPrefix/Expression
|
//Expression/ConditionalAndExpression/PrimaryExpression/PrimaryPrefix/Expression[
    count(*)=1 and
    count(./CastExpression)=0 and
    count(./EqualityExpression/MultiplicativeExpression)=0 and
    count(./ConditionalExpression[@Ternary='true'])=0 and
    count(./ConditionalOrExpression)=0]
|
//Expression/ConditionalOrExpression/PrimaryExpression/PrimaryPrefix/Expression[
    count(*)=1 and
    not(./CastExpression) and
    not(./ConditionalExpression[@Ternary='true']) and
    not(./EqualityExpression/MultiplicativeExpression)]
|
//Expression/ConditionalExpression/PrimaryExpression/PrimaryPrefix/Expression[
    count(*)=1 and
    not(./CastExpression) and
    not(./EqualityExpression)]
|
//Expression/AdditiveExpression[not(./PrimaryExpression/PrimaryPrefix/Literal[@StringLiteral='true'])]
  /PrimaryExpression[1]/PrimaryPrefix/Expression[
    count(*)=1 and
    not(./CastExpression) and
    not(./AdditiveExpression[@Image = '-']) and
    not(./ShiftExpression) and
    not(./RelationalExpression) and
    not(./InstanceOfExpression) and
    not(./EqualityExpression) and
    not(./AndExpression) and
    not(./ExclusiveOrExpression) and
    not(./InclusiveOrExpression) and
    not(./ConditionalAndExpression) and
    not(./ConditionalOrExpression) and
    not(./ConditionalExpression)]
|
//Expression/EqualityExpression/PrimaryExpression/PrimaryPrefix/Expression[
    count(*)=1 and
    not(./CastExpression) and
    not(./AndExpression) and
    not(./InclusiveOrExpression) and
    not(./ExclusiveOrExpression) and
    not(./ConditionalExpression) and
    not(./ConditionalAndExpression) and
    not(./ConditionalOrExpression) and
    not(./EqualityExpression)]

Example(s):

public class Foo {

    private int _bar1;
    private Integer _bar2;

    public void setBar(int n) {
        _bar1 = Integer.valueOf((n)); // here
        _bar2 = (n); // and here
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/UselessParentheses" />

UselessQualifiedThis

Since: PMD 5.4.0

Priority: Medium (3)

Look for qualified this usages in the same class.

This rule is defined by the following XPath expression:

//PrimaryExpression
[PrimaryPrefix/Name[@Image]]
[PrimarySuffix[@Arguments='false']]
[not(PrimarySuffix/MemberSelector)]
[ancestor::ClassOrInterfaceBodyDeclaration[1][@AnonymousInnerClass='false']]
/PrimaryPrefix/Name[@Image = ancestor::ClassOrInterfaceDeclaration[1]/@Image]

Example(s):

public class Foo {
    final Foo otherFoo = Foo.this;  // use "this" directly

    public void doSomething() {
         final Foo anotherFoo = Foo.this;  // use "this" directly
    }

    private ActionListener returnListener() {
        return new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                doSomethingWithQualifiedThis(Foo.this);  // This is fine
            }
        };
    }

    private class Foo3 {
        final Foo myFoo = Foo.this;  // This is fine
    }

    private class Foo2 {
        final Foo2 myFoo2 = Foo2.this;  // Use "this" direclty
    }
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/UselessQualifiedThis" />

VariableNamingConventions

Since: PMD 1.2

Priority: High (1)

A variable naming conventions rule - customize this to your liking. Currently, it checks for final variables that should be fully capitalized and non-final variables that should not include underscores.

This rule is defined by the following Java class: net.sourceforge.pmd.lang.java.rule.codestyle.VariableNamingConventionsRule

Example(s):

public class Foo {
    public static final int MY_NUM = 0;
    public String myTest = "";
    DataModule dmTest = new DataModule();
}

This rule has the following properties:

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/VariableNamingConventions" />

WhileLoopsMustUseBraces

Deprecated

Since: PMD 0.7

Priority: Medium (3)

Avoid using ‘while’ statements without using braces to surround the code block. If the code formatting or indentation is lost then it becomes difficult to separate the code being controlled from the rest.

This rule is defined by the following XPath expression:

//WhileStatement[not(Statement/Block)]

Example(s):

while (true)    // not recommended
      x++;
      
while (true) {  // preferred approach
      x++;
}

Use this rule by referencing it:

<rule ref="category/java/codestyle.xml/WhileLoopsMustUseBraces" />