AnnotatedElement-Interface-java.lang.reflect-Java API参考

public interface AnnotatedElement

Represents an annotated element of the program currently running in this VM. This interface allows annotations to be read reflectively. All annotations returned by methods in this interface are immutable and serializable. The arrays returned by methods of this interface may be modified by callers without affecting the arrays returned to other callers.

The getAnnotationsByType(java.lang.Class) and getDeclaredAnnotationsByType(java.lang.Class) methods support multiple annotations of the same type on an element. If the argument to either method is a repeatable annotation type (JLS 9.6), then the method will "look through" a container annotation (JLS 9.7), if present, and return any annotations inside the container. Container annotations may be generated at compile-time to wrap multiple annotations of the argument type.

The terms directly present, indirectly present, present, and associated are used throughout this interface to describe precisely which annotations are returned by methods:

An annotation A is directly present on an element E if E has a RuntimeVisibleAnnotations or RuntimeVisibleParameterAnnotations or RuntimeVisibleTypeAnnotations attribute, and the attribute contains A.
An annotation A is indirectly present on an element E if E has a RuntimeVisibleAnnotations or RuntimeVisibleParameterAnnotations or RuntimeVisibleTypeAnnotations attribute, and A 's type is repeatable, and the attribute contains exactly one annotation whose value element contains A and whose type is the containing annotation type of A 's type.
An annotation A is present on an element E if either:
- A is directly present on E; or
- No annotation of A 's type is directly present on E, and E is a class, and A 's type is inheritable, and A is present on the superclass of E.
An annotation A is associated with an element E if either:
- A is directly or indirectly present on E; or
- No annotation of A 's type is directly or indirectly present on E, and E is a class, and A's type is inheritable, and A is associated with the superclass of E.

The table below summarizes which kind of annotation presence different methods in this interface examine.

For an invocation of get[Declared]AnnotationsByType( Class < T >), the order of annotations which are directly or indirectly present on an element E is computed as if indirectly present annotations on E are directly present on E in place of their container annotation, in the order in which they appear in the value element of the container annotation.

There are several compatibility concerns to keep in mind if an annotation type T is originally not repeatable and later modified to be repeatable. The containing annotation type for T is TC.

Modifying T to be repeatable is source and binary compatible with existing uses of T and with existing uses of TC. That is, for source compatibility, source code with annotations of type T or of type TC will still compile. For binary compatibility, class files with annotations of type T or of type TC (or with other kinds of uses of type T or of type TC) will link against the modified version of T if they linked against the earlier version. (An annotation type TC may informally serve as an acting containing annotation type before T is modified to be formally repeatable. Alternatively, when T is made repeatable, TC can be introduced as a new type.)
If an annotation type TC is present on an element, and T is modified to be repeatable with TC as its containing annotation type then:
- The change to T is behaviorally compatible with respect to the get[Declared]Annotation(Class<T>) (called with an argument of T or TC) and get[Declared]Annotations() methods because the results of the methods will not change due to TC becoming the containing annotation type for T.
- The change to T changes the results of the get[Declared]AnnotationsByType(Class<T>) methods called with an argument of T, because those methods will now recognize an annotation of type TC as a container annotation for T and will "look through" it to expose annotations of type T.
If an annotation of type T is present on an element and T is made repeatable and more annotations of type T are added to the element:
- The addition of the annotations of type T is both source compatible and binary compatible.
- The addition of the annotations of type T changes the results of the get[Declared]Annotation(Class<T>) methods and get[Declared]Annotations() methods, because those methods will now only see a container annotation on the element and not see an annotation of type T.
- The addition of the annotations of type T changes the results of the get[Declared]AnnotationsByType(Class<T>) methods, because their results will expose the additional annotations of type T whereas previously they exposed only a single annotation of type T.

If an annotation returned by a method in this interface contains (directly or indirectly) a Class-valued member referring to a class that is not accessible in this VM, attempting to read the class by calling the relevant Class-returning method on the returned annotation will result in a TypeNotPresentException.

Similarly, attempting to read an enum-valued member will result in a EnumConstantNotPresentException if the enum constant in the annotation is no longer present in the enum type.

If an annotation type T is (meta-)annotated with an @Repeatable annotation whose value element indicates a type TC, but TC does not declare a value() method with a return type of T[], then an exception of type AnnotationFormatError is thrown.

Finally, attempting to read a member whose definition has evolved incompatibly will result in a AnnotationTypeMismatchException or an IncompleteAnnotationException.

Since:

1.5

Method Summary

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Modifier and Type	Method	Description
<T extends Annotation>T	getAnnotation(Class<T> annotationClass)	Returns this element's annotation for the specified type if such an annotation is present, else null.
Annotation[]	getAnnotations()	Returns annotations that are present on this element.
default <T extends Annotation>T[]	getAnnotationsByType(Class<T> annotationClass)	Returns annotations that are associated with this element.
default <T extends Annotation>T	getDeclaredAnnotation(Class<T> annotationClass)	Returns this element's annotation for the specified type if such an annotation is directly present, else null.
Annotation[]	getDeclaredAnnotations()	Returns annotations that are directly present on this element.
default <T extends Annotation>T[]	getDeclaredAnnotationsByType(Class<T> annotationClass)	Returns this element's annotation(s) for the specified type if such annotations are either directly present or indirectly present.
default boolean	isAnnotationPresent(Class<? extends Annotation> annotationClass)	Returns true if an annotation for the specified type is present on this element, else false.

Method Detail

isAnnotationPresent

default boolean isAnnotationPresent(Class<? extends Annotation> annotationClass)

Returns true if an annotation for the specified type is present on this element, else false. This method is designed primarily for convenient access to marker annotations.

The truth value returned by this method is equivalent to: getAnnotation(annotationClass) != null

The body of the default method is specified to be the code above.

Parameters:

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Parameter Name	Parameter Description
annotationClass	the Class object corresponding to the annotation type

Returns:

true if an annotation for the specified annotation type is present on this element, else false

Throws:

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Throw Name	Throw Description
NullPointerException	if the given annotation class is null

Since:

1.5

getAnnotation

<T extends Annotation> T getAnnotation(Class<T> annotationClass)

Returns this element's annotation for the specified type if such an annotation is present, else null.

Type Parameters:

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Type Parameter Name	Type Parameter Description
T	the type of the annotation to query for and return if present

Parameters:

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Parameter Name	Parameter Description
annotationClass	the Class object corresponding to the annotation type

Returns:

this element's annotation for the specified annotation type if present on this element, else null

Throws:

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Throw Name	Throw Description
NullPointerException	if the given annotation class is null

Since:

1.5

getAnnotations

Annotation[] getAnnotations()

Returns annotations that are present on this element. If there are no annotations present on this element, the return value is an array of length 0. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.

Returns:

annotations present on this element

Since:

1.5

getAnnotationsByType

default <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass)

Returns annotations that are associated with this element. If there are no annotations associated with this element, the return value is an array of length 0. The difference between this method and getAnnotation(java.lang.Class) is that this method detects if its argument is a repeatable annotation type (JLS 9.6), and if so, attempts to find one or more annotations of that type by "looking through" a container annotation. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.

Type Parameters:

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Type Parameter Name	Type Parameter Description
T	the type of the annotation to query for and return if present

Parameters:

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Parameter Name	Parameter Description
annotationClass	the Class object corresponding to the annotation type

Returns:

all this element's annotations for the specified annotation type if associated with this element, else an array of length zero

Throws:

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Throw Name	Throw Description
NullPointerException	if the given annotation class is null

Since:

1.8

getDeclaredAnnotation

default <T extends Annotation> T getDeclaredAnnotation(Class<T> annotationClass)

Returns this element's annotation for the specified type if such an annotation is directly present, else null. This method ignores inherited annotations. (Returns null if no annotations are directly present on this element.)

Type Parameters:

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Type Parameter Name	Type Parameter Description
T	the type of the annotation to query for and return if directly present

Parameters:

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Parameter Name	Parameter Description
annotationClass	the Class object corresponding to the annotation type

Returns:

this element's annotation for the specified annotation type if directly present on this element, else null

Throws:

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Throw Name	Throw Description
NullPointerException	if the given annotation class is null

Since:

1.8

getDeclaredAnnotationsByType

default <T extends Annotation> T[] getDeclaredAnnotationsByType(Class<T> annotationClass)

Returns this element's annotation(s) for the specified type if such annotations are either directly present or indirectly present. This method ignores inherited annotations. If there are no specified annotations directly or indirectly present on this element, the return value is an array of length 0. The difference between this method and getDeclaredAnnotation(java.lang.Class) is that this method detects if its argument is a repeatable annotation type (JLS 9.6), and if so, attempts to find one or more annotations of that type by "looking through" a container annotation if one is present. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.

Type Parameters:

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Type Parameter Name	Type Parameter Description
T	the type of the annotation to query for and return if directly or indirectly present

Parameters:

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Parameter Name	Parameter Description
annotationClass	the Class object corresponding to the annotation type

Returns:

all this element's annotations for the specified annotation type if directly or indirectly present on this element, else an array of length zero

Throws:

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Throw Name	Throw Description
NullPointerException	if the given annotation class is null

Since:

1.8

getDeclaredAnnotations

Annotation[] getDeclaredAnnotations()

Returns annotations that are directly present on this element. This method ignores inherited annotations. If there are no annotations directly present on this element, the return value is an array of length 0. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.

Returns:

annotations directly present on this element

Since:

1.5