java注解

1 @Target(ElementType.METHOD)
2 @Retention(RetentionPolicy.RUNTIME)
3 public @interface MyMethodAnnotation {
4 
5 }

 1 public class AnnotationDemo {
 2 
 3     @MyMethodAnnotation
 4     public void test() {
 5         
 6     }
 7     
 8     @MyMethodAnnotation
 9     public void test2() {
10         
11     }
12     
13     public void test3() {
14         
15     }
16 }

 1 public class Client {
 2 
 3     public static void main(String[] args) {
 4         Method[] methods = AnnotationDemo.class.getMethods();
 5         for(Method m : methods) {
 6             if(m.isAnnotationPresent(MyMethodAnnotation.class)) {
 7                 System.out.println("----- " + m.getName() + " -------");
 8             }
 9         }
10     }
11 }

----- test -------
----- test2 -------

public enum ElementType {
    /** Class, interface (including annotation type), or enum declaration */
    TYPE, // 用于描述类、接口(包括注解类型) 或enum声明

    /** Field declaration (includes enum constants) */
    FIELD, // 用于描述域

    /** Method declaration */
    METHOD, // 用于描述方法

    /** Parameter declaration */
    PARAMETER, // 用于描述参数

    /** Constructor declaration */
    CONSTRUCTOR, // 用于描述构造函数

    /** Local variable declaration */
    LOCAL_VARIABLE, // 用于描述局部变量

    /** Annotation type declaration */
    ANNOTATION_TYPE,

    /** Package declaration */
    PACKAGE // 用于描述包
}

public enum RetentionPolicy {
    /**
     * Annotations are to be discarded by the compiler.
     */
    SOURCE,  //在源文件有效 保留在源文件

    /**
     * Annotations are to be recorded in the class file by the compiler
     * but need not be retained by the VM at run time.  This is the default
     * behavior.
     */
    CLASS, //在class文件有效 保留在class文件

    /**
     * Annotations are to be recorded in the class file by the compiler and
     * retained by the VM at run time, so they may be read reflectively.
     *
     * @see java.lang.reflect.AnnotatedElement
     */
    RUNTIME //在运行时有效 运行时保留
}