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Stuff related to Java Annotations and Annotation Processing
Define an Annotation
@Retention(RUNTIME) //RetentionPolicy
@Target(TYPE) //ElementType
public @interface MyAnnot {
boolean value() default false;
String name();
}
|
Annotation for Classes, Eums and Interfaces available for Reflection
RetentionPolicy
CLASS
|
Compiled into .class No Reflection |
RUNTIME
|
Available for Reflection |
SOURCE
|
Only in Source Dropped for Compilation |
ElementType
TYPE
|
Class, Interface, Enum |
FIELD
|
Class fields |
METHOD
|
Methods no Constructor |
PARAMETER
|
Any Param of a Method/Constructor |
CONSTRUCTOR
|
Only Constructors |
LOCAL_VARIABLE
|
only Local Vars |
ANNOTATION_TYPE
|
valid for other Annotations |
PACKAGE
|
Annotation for Package |
PACKAGE annotations should only be in package-info.java
|
|
Extract Annotation from Class
getAnnotation(Class<A> aClass)
|
in this class or from parent |
getDeclaredAnnotation(Class<A> aClass)
|
only declared in this class |
getAnnotations()
|
array of Annotations |
getDeclaredAnnotations()
|
array of Annotations |
Extract Fields and Methods
get[Declared]Field(String name)
|
extracts a Field |
get[Declared]Method(String name, Class<?>... parameterTypes)
|
extracts a Method |
getConstructors()
|
extracts an Array of Constructor |
get[Declared]Fields()
|
extracts an Array of Field |
get[Declared]Methods()
|
extracts an Array of Method |
getDeclared... always points to exactly this Object only including private, without Declared any super can also match but only public ones.
Extract Field information
getName()
|
getType()
|
getModifiers()
|
get(Object obj)
|
extract field value from obj |
set(Object obj, Object val)
|
set field to value |
Primitives are available e.g.: getInt(obj), setInt(obj, val)
Method Functions
getName()
|
getParameterTypes()
|
Class Array of Types
|
getReturnType()
|
invoke(Object obj, Object... args)
|
Call Method |
Constructors
Object.class.newInstance()
|
utilizes Default Constructor of an Class object |
const.newInstance(Object.... args)
|
utilizes one of the extracted Constructors |
|
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