checkstyle – Annotations

Content

Content
AnnotationLocation
AnnotationOnSameLine
AnnotationUseStyle
MissingDeprecated
MissingOverride
PackageAnnotation
SuppressWarnings
SuppressWarningsHolder

AnnotationLocation

Since Checkstyle 6.0

Description

Checks location of annotation on language elements. By default, Check enforce to locate annotations immediately after documentation block and before target element, annotation should be located on separate line from target element. This check also verifies that the annotations are on the same indenting level as the annotated element if they are not on the same line.

Attention: Elements that cannot have JavaDoc comments like local variables are not in the scope of this check even though a token type like VARIABLE_DEF would match them.

Attention: Annotations among modifiers are ignored (looks like false-negative) as there might be a problem with annotations for return types:

public @Nullable Long getStartTimeOrNull() { ... }

Such annotations are better to keep close to type. Due to limitations, Checkstyle can not examine the target of an annotation.

Example:

@Override
@Nullable
public String getNameIfPresent() { ... }

Properties

name	description	type	default value	since
allowSamelineMultipleAnnotations	Allow annotation(s) to be located on the same line as target element.	boolean	`false`	6.0
allowSamelineSingleParameterlessAnnotation	Allow single parameterless annotation to be located on the same line as target element.	boolean	`true`	6.1
allowSamelineParameterizedAnnotation	Allow one and only parameterized annotation to be located on the same line as target element.	boolean	`false`	6.4
tokens	tokens to check	subset of tokens CLASS_DEF , INTERFACE_DEF , PACKAGE_DEF , ENUM_CONSTANT_DEF , ENUM_DEF , METHOD_DEF , CTOR_DEF , VARIABLE_DEF , ANNOTATION_DEF , ANNOTATION_FIELD_DEF , RECORD_DEF , COMPACT_CTOR_DEF .	CLASS_DEF , INTERFACE_DEF , PACKAGE_DEF , ENUM_CONSTANT_DEF , ENUM_DEF , METHOD_DEF , CTOR_DEF , VARIABLE_DEF , RECORD_DEF , COMPACT_CTOR_DEF .	6.0

Examples

To configure the default check to allow one single parameterless annotation on the same line:

<module name="AnnotationLocation"/>

Example for above configuration:

@NotNull private boolean field1; //ok
@Override public int hashCode() { return 1; } //ok
@NotNull //ok
private boolean field2;
@Override //ok
public boolean equals(Object obj) { return true; }
@Mock DataLoader loader; //ok
@SuppressWarnings("deprecation") DataLoader loader; //violation
@SuppressWarnings("deprecation") public int foo() { return 1; } //violation
@NotNull @Mock DataLoader loader; //violation

Use the following configuration to allow multiple annotations on the same line:

<module name="AnnotationLocation">
  <property name="allowSamelineMultipleAnnotations" value="true"/>
  <property name="allowSamelineSingleParameterlessAnnotation"
    value="false"/>
  <property name="allowSamelineParameterizedAnnotation" value="false"/>
</module>

Example to allow any location multiple annotations:

@NotNull private boolean field1; //ok
@Override public int hashCode() { return 1; } //ok
@NotNull //ok
private boolean field2;
@Override //ok
public boolean equals(Object obj) { return true; }
@Mock DataLoader loader; //ok
@SuppressWarnings("deprecation") DataLoader loader; //ok
@SuppressWarnings("deprecation") public int foo() { return 1; } //ok
@NotNull @Mock DataLoader loader; //ok

Use the following configuration to allow only one and only parameterized annotation on the same line:

<module name="AnnotationLocation">
  <property name="allowSamelineMultipleAnnotations" value="false"/>
  <property name="allowSamelineSingleParameterlessAnnotation"
    value="false"/>
  <property name="allowSamelineParameterizedAnnotation" value="true"/>
</module>

Example to allow only one and only parameterized annotation on the same line:

@NotNull private boolean field1; //violation
@Override public int hashCode() { return 1; } //violation
@NotNull //ok
private boolean field2;
@Override //ok
public boolean equals(Object obj) { return true; }
@Mock DataLoader loader; //violation
@SuppressWarnings("deprecation") DataLoader loader; //ok
@SuppressWarnings("deprecation") public int foo() { return 1; } //ok
@NotNull @Mock DataLoader loader; //violation

Use the following configuration to only validate annotations on methods to allow one single parameterless annotation on the same line:

<module name="AnnotationLocation">
  <property name="tokens" value="METHOD_DEF"/>
  <property name="allowSamelineMultipleAnnotations" value="false"/>
  <property name="allowSamelineSingleParameterlessAnnotation"
    value="true"/>
  <property name="allowSamelineParameterizedAnnotation" value="false"/>
</module>

Example for above configuration to check only methods:

@NotNull private boolean field1; //ok
@Override public int hashCode() { return 1; } //ok
@NotNull //ok
private boolean field2;
@Override //ok
public boolean equals(Object obj) { return true; }
@Mock DataLoader loader; //ok
@SuppressWarnings("deprecation") DataLoader loader; //ok
@SuppressWarnings("deprecation") public int foo() { return 1; } //violation
@NotNull @Mock DataLoader loader; //ok

Example of Usage

Violation Messages

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.annotation

Parent Module

TreeWalker

AnnotationOnSameLine

Since Checkstyle 8.2

Description

Checks that annotations are located on the same line with their targets. Verifying with this check is not good practice, but it is using by some style guides.

Properties

name	description	type	default value	since
tokens	tokens to check	subset of tokens CLASS_DEF , INTERFACE_DEF , ENUM_DEF , METHOD_DEF , CTOR_DEF , VARIABLE_DEF , PARAMETER_DEF , ANNOTATION_DEF , TYPECAST , LITERAL_THROWS , IMPLEMENTS_CLAUSE , TYPE_ARGUMENT , LITERAL_NEW , DOT , ANNOTATION_FIELD_DEF , RECORD_DEF , COMPACT_CTOR_DEF .	CLASS_DEF , INTERFACE_DEF , ENUM_DEF , METHOD_DEF , CTOR_DEF , VARIABLE_DEF , RECORD_DEF , COMPACT_CTOR_DEF .	8.2

Examples

To configure the check:

<module name="AnnotationOnSameLine"/>

Example:

class Foo {

  @SuppressWarnings("deprecation")  // violation, annotation should be on the same line
  public Foo() {
  }

  @SuppressWarnings("unchecked") public void fun2() {  // OK
  }

}

@SuppressWarnings("unchecked") class Bar extends Foo {  // OK

  @Deprecated public Bar() {  // OK
  }

  @Override  // violation, annotation should be on the same line
  public void fun1() {
  }

  @Before @Override public void fun2() {  // OK
  }

  @SuppressWarnings("deprecation")  // violation, annotation should be on the same line
  @Before public void fun3() {
  }

}

To configure the check to check for annotations applied on interfaces, variables and constructors:

<module name="AnnotationOnSameLine">
  <property name="tokens"
      value="INTERFACE_DEF, VARIABLE_DEF, CTOR_DEF"/>
</module>

Example:

@Deprecated interface Foo {  // OK

  void doSomething();

}

class Bar implements Foo {

  @SuppressWarnings("deprecation")  // violation, annotation should be on the same line
  public Bar() {
  }

  @Override  // OK
  public void doSomething() {
  }

  @Nullable  // violation, annotation should be on the same line
  String s;

}

Example of Usage

Checkstyle Style

Violation Messages

annotation.same.line

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.annotation

Parent Module

TreeWalker

AnnotationUseStyle

Since Checkstyle 5.0

Description

Checks the style of elements in annotations.

Annotations have three element styles starting with the least verbose.

ElementStyleOption.COMPACT_NO_ARRAY
ElementStyleOption.COMPACT
ElementStyleOption.EXPANDED

To not enforce an element style a ElementStyleOption.IGNORE type is provided. The desired style can be set through the elementStyle property.

Using the ElementStyleOption.EXPANDED style is more verbose. The expanded version is sometimes referred to as "named parameters" in other languages.

Using the ElementStyleOption.COMPACT style is less verbose. This style can only be used when there is an element called 'value' which is either the sole element or all other elements have default values.

Using the ElementStyleOption.COMPACT_NO_ARRAY style is less verbose. It is similar to the ElementStyleOption.COMPACT style but single value arrays are flagged. With annotations a single value array does not need to be placed in an array initializer.

The ending parenthesis are optional when using annotations with no elements. To always require ending parenthesis use the ClosingParensOption.ALWAYS type. To never have ending parenthesis use the ClosingParensOption.NEVER type. To not enforce a closing parenthesis preference a ClosingParensOption.IGNORE type is provided. Set this through the closingParens property.

Annotations also allow you to specify arrays of elements in a standard format. As with normal arrays, a trailing comma is optional. To always require a trailing comma use the TrailingArrayCommaOption.ALWAYS type. To never have a trailing comma use the TrailingArrayCommaOption.NEVER type. To not enforce a trailing array comma preference a TrailingArrayCommaOption.IGNORE type is provided. Set this through the trailingArrayComma property.

By default the ElementStyleOption is set to COMPACT_NO_ARRAY, the TrailingArrayCommaOption is set to NEVER, and the ClosingParensOption is set to NEVER.

According to the JLS, it is legal to include a trailing comma in arrays used in annotations but Sun's Java 5 & 6 compilers will not compile with this syntax. This may in be a bug in Sun's compilers since eclipse 3.4's built-in compiler does allow this syntax as defined in the JLS. Note: this was tested with compilers included with JDK versions 1.5.0.17 and 1.6.0.11 and the compiler included with eclipse 3.4.1.

See Java Language specification, §9.7.

Properties

name	description	type	default value	since
elementStyle	Define the annotation element styles.	ElementStyleOption	`compact_no_array`	5.0
closingParens	Define the policy for ending parenthesis.	ClosingParensOption	`never`	5.0
trailingArrayComma	Define the policy for trailing comma in arrays.	TrailingArrayCommaOption	`never`	5.0

Examples

To configure the check:

<module name="AnnotationUseStyle"/>

Example:

@Deprecated // OK
@SomeArrays(pooches={DOGS.LEO}) // Violation - COMPACT_NO_ARRAY
@SuppressWarnings({""}) // Violation - COMPACT_NO_ARRAY
public class TestOne
{

}

@SomeArrays(pooches={DOGS.LEO}, um={}, test={"bleh"}) // Violation - COMPACT_NO_ARRAY
@SuppressWarnings("") // OK
@Deprecated() // Violation - cannot have closing parenthesis
class TestTwo {

}

To configure the check to enforce an expanded style, with a trailing array comma set to never and always including the closing parenthesis.

<module name="AnnotationUseStyle">
  <property name="elementStyle" value="expanded"/>
  <property name="trailingArrayComma" value="never"/>
  <property name="closingParens" value="always"/>
</module>

Example:

@Deprecated // Violation - must have closing parenthesis
@SomeArrays(pooches={DOGS.LEO}) // OK
@SuppressWarnings({""}) // Violation - EXPANDED
public class TestOne
{

}

@SomeArrays(pooches={DOGS.LEO}, um={}, test={"bleh"}) // OK
@SuppressWarnings("") // Violation - EXPANDED
@Deprecated() // OK
class TestTwo {

}

Example of Usage

Checkstyle Style

Violation Messages

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.annotation

Parent Module

TreeWalker

MissingDeprecated

Since Checkstyle 5.0

Description

Verifies that the annotation @Deprecated and the Javadoc tag @deprecated are both present when either of them is present.

Both ways of flagging deprecation serve their own purpose. The @Deprecated annotation is used for compilers and development tools. The @deprecated javadoc tag is used to document why something is deprecated and what, if any, alternatives exist.

In order to properly mark something as deprecated both forms of deprecation should be present.

Package deprecation is a exception to the rule of always using the javadoc tag and annotation to deprecate. It is not clear if the javadoc tool will support it or not as newer versions keep flip flopping on if it is supported or will cause an error. See JDK-8160601. The deprecated javadoc tag is currently the only way to say why the package is deprecated and what to use instead. Until this is resolved, if you don't want to print violations on package-info, you can use a filter to ignore these files until the javadoc tool faithfully supports it. An example config using SuppressionSingleFilter is:

<!-- required till https://bugs.openjdk.java.net/browse/JDK-8160601 -->
<module name="SuppressionSingleFilter">
    <property name="checks" value="MissingDeprecatedCheck"/>
    <property name="files" value="package-info\.java"/>
</module>

Properties

name	description	type	default value	since
violateExecutionOnNonTightHtml	Control when to print violations if the Javadoc being examined by this check violates the tight html rules defined at Tight-HTML Rules.	boolean	`false`	8.24

Examples

To configure the check:

<module name="MissingDeprecated"/>

Examples of validating source code:

@Deprecated
public static final int MY_CONST = 123456; // no violation

/** This javadoc is missing deprecated tag. */
@Deprecated
public static final int COUNTER = 10; // violation

Example of Usage

Checkstyle Style

Violation Messages

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.annotation

Parent Module

TreeWalker

MissingOverride

Since Checkstyle 5.0

Description

Verifies that the @Override annotation is present when the @inheritDoc javadoc tag is present.

Rationale: The @Override annotation helps compiler tools ensure that an override is actually occurring. It is quite easy to accidentally overload a method or hide a static method and using the @Override annotation points out these problems.

This check will log a violation if using the @inheritDoc tag on a method that is not valid (ex: private, or static method).

There is a slight difference between the @Override annotation in Java 5 versus Java 6 and above. In Java 5, any method overridden from an interface cannot be annotated with @Override. In Java 6 this behavior is allowed.

As a result of the aforementioned difference between Java 5 and Java 6, a property called javaFiveCompatibility is available. This property will only check classes, interfaces, etc. that do not contain the extends or implements keyword or are not anonymous classes. This means it only checks methods overridden from java.lang.Object. Java 5 Compatibility mode severely limits this check. It is recommended to only use it on Java 5 source.

Properties

name	description	type	default value	since
javaFiveCompatibility	Enable java 5 compatibility mode.	boolean	`false`	5.0

Examples

To configure the check:

<module name="MissingOverride"/>

Example:

class Test extends SuperClass {

    /** {@inheritDoc} */
    @Override
    public void test1() { // OK

    }

    /** {@inheritDoc} */
    public void test2() { // violation, should be annotated with @Override

    }

    /** {@inheritDoc} */
    private void test3() { // violation, using the @inheritDoc tag on private method

    }

    /** {@inheritDoc} */
    public static void test4() { // violation, using the @inheritDoc tag on static method

    }
}

To configure the check for the javaFiveCompatibility mode:

<module name="MissingOverride">
  <property name="javaFiveCompatibility"
      value="true"/>
</module>

Example:

class Test1 {

    /** {@inheritDoc} */
    public void equals() { // violation, should be annotated with @Override

    }
}

interface Test2 {

    /** {@inheritDoc} */
    void test(); // violation, should be annotated with @Override
}

class Test3 extends SuperClass {

    /** {@inheritDoc} */
    public void test() { // OK, is ignored because class extends other class

    }
}

class Test4 implements SuperInterface {

    /** {@inheritDoc} */
    public void test() { // OK, is ignored because class implements interface

    }
}

class Test5 {
    Runnable r = new Runnable() {

        /** {@inheritDoc} */
        public void run() { // OK, is ignored because class is anonymous class

        }
    };
}

Example of Usage

Checkstyle Style

Violation Messages

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.annotation

Parent Module

TreeWalker

PackageAnnotation

Since Checkstyle 5.0

Description

Checks that all package annotations are in the package-info.java file.

For Java SE8 and above, placement of package annotations in the package-info.java file is enforced by the compiler and this check is not necessary.

For Java SE7 and below, the Java Language Specification highly recommends but doesn't require that annotations are placed in the package-info.java file, and this check can help to enforce that placement.

See Java Language Specification, §7.4.1 for more info.

Examples

To configure the check:

 <module name="PackageAnnotation"/>

Example of validating MyClass.java:

@Deprecated
package com.example.annotations.packageannotation; //violation

Example of fixing violation in MyClass.java:

package com.example.annotations.packageannotation; //ok

Example of validating package-info.java:

@Deprecated
package com.example.annotations.packageannotation; //ok

Example of Usage

Checkstyle Style

Violation Messages

annotation.package.location

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.annotation

Parent Module

TreeWalker

SuppressWarnings

Since Checkstyle 5.0

Description

Allows to specify what warnings that @SuppressWarnings is not allowed to suppress. You can also specify a list of TokenTypes that the configured warning(s) cannot be suppressed on.

Limitations: This check does not consider conditionals inside the @SuppressWarnings annotation.

For example: @SuppressWarnings((false) ? (true) ? "unchecked" : "foo" : "unused"). According to the above example, the "unused" warning is being suppressed not the "unchecked" or "foo" warnings. All of these warnings will be considered and matched against regardless of what the conditional evaluates to. The check also does not support code like @SuppressWarnings("un" + "used"), @SuppressWarnings((String) "unused") or @SuppressWarnings({('u' + (char)'n') + (""+("used" + (String)"")),}).

By default, any warning specified will be disallowed on all legal TokenTypes unless otherwise specified via the tokens property.

Also, by default warnings that are empty strings or all whitespace (regex: ^$|^\s+$) are flagged. By specifying, the format property these defaults no longer apply.

This check can be configured so that the "unchecked" and "unused" warnings cannot be suppressed on anything but variable and parameter declarations. See below of an example.

Properties

name	description	type	default value	since
format	Specify the RegExp to match against warnings. Any warning being suppressed matching this pattern will be flagged.	Pattern	`"^\s*+$"`	5.0
tokens	tokens to check	subset of tokens CLASS_DEF , INTERFACE_DEF , ENUM_DEF , ANNOTATION_DEF , ANNOTATION_FIELD_DEF , ENUM_CONSTANT_DEF , PARAMETER_DEF , VARIABLE_DEF , METHOD_DEF , CTOR_DEF , COMPACT_CTOR_DEF , RECORD_DEF .	CLASS_DEF , INTERFACE_DEF , ENUM_DEF , ANNOTATION_DEF , ANNOTATION_FIELD_DEF , ENUM_CONSTANT_DEF , PARAMETER_DEF , VARIABLE_DEF , METHOD_DEF , CTOR_DEF , COMPACT_CTOR_DEF , RECORD_DEF .	5.0

Examples

To configure the check:

 <module name="SuppressWarnings"/>

To configure the check so that the "unchecked" and "unused" warnings cannot be suppressed on anything but variable and parameter declarations.

<module name="SuppressWarnings">
  <property name="format"
      value="^unchecked$|^unused$"/>
  <property name="tokens"
    value="
    CLASS_DEF,INTERFACE_DEF,ENUM_DEF,
    ANNOTATION_DEF,ANNOTATION_FIELD_DEF,
    ENUM_CONSTANT_DEF,METHOD_DEF,CTOR_DEF
    "/>
</module>

Example of Usage

Checkstyle Style

Violation Messages

suppressed.warning.not.allowed

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.annotation

Parent Module

TreeWalker

SuppressWarningsHolder

Since Checkstyle 5.7

Description

Maintains a set of check suppressions from @SuppressWarnings annotations. It allows to prevent Checkstyle from reporting violations from parts of code that were annotated with @SuppressWarnings and using name of the check to be excluded. You can also define aliases for check names that need to be suppressed.

Properties

name	description	type	default value	since
aliasList	Specify aliases for check names that can be used in code within `SuppressWarnings`.	String[] in a format of comma separated attribute=value entries. The attribute is the fully qualified name of the Check and value is its alias.	`null`	5.7

Examples

To prevent FooCheck violations from being reported write:

@SuppressWarnings("foo") interface I { }
@SuppressWarnings("foo") enum E { }
@SuppressWarnings("foo") InputSuppressWarningsFilter() { }

Some real check examples:

This will prevent from invocation of the MemberNameCheck:

@SuppressWarnings({"membername"})
private int J;

You can also use a checkstyle prefix to prevent compiler from processing this annotations. For example this will prevent ConstantNameCheck:

@SuppressWarnings("checkstyle:constantname")
private static final int m = 0;

The general rule is that the argument of the @SuppressWarnings will be matched against class name of the checker in lower case and without Check suffix if present.

If aliasList property was provided you can use your own names e.g below code will work if there was provided a ParameterNumberCheck=paramnum in the aliasList:

@SuppressWarnings("paramnum")
public void needsLotsOfParameters(@SuppressWarnings("unused") int a,
  int b, int c, int d, int e, int f, int g, int h) {
  ...
}

It is possible to suppress all the checkstyle warnings with the argument "all":

@SuppressWarnings("all")
public void someFunctionWithInvalidStyle() {
  //...
}

Example of Usage

Checkstyle Style

Package

com.puppycrawl.tools.checkstyle.checks

Parent Module

TreeWalker

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Content

AnnotationLocation

Description

Properties

Examples

Example of Usage

Violation Messages

Package

Parent Module

AnnotationOnSameLine

Description

Properties

Examples

Example of Usage

Violation Messages

Package

Parent Module

AnnotationUseStyle

Description

Properties

Examples

Example of Usage

Violation Messages

Package

Parent Module

MissingDeprecated

Description

Properties

Examples

Example of Usage

Violation Messages

Package

Parent Module

MissingOverride

Description

Properties

Examples

Example of Usage

Violation Messages

Package

Parent Module

PackageAnnotation

Description

Examples

Example of Usage

Violation Messages

Package

Parent Module

SuppressWarnings

Description

Properties

Examples

Example of Usage

Violation Messages

Package

Parent Module

SuppressWarningsHolder

Description

Properties

Examples

Example of Usage

Package

Parent Module