如何自定义注解(how to customize the annotation in java)

/**
     * Annotations are to be discarded by the compiler.
     */
    SOURCE,

    /**
     * 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,

    /**
     * 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

public enum ElementType {
    /** Class, interface (including annotation type), or enum declaration */
    TYPE, 

    /** Field declaration (includes enum constants) */
    FIELD,

    /** Method declaration */
    METHOD,

    /** Formal parameter declaration */
    PARAMETER,

    /** Constructor declaration */
    CONSTRUCTOR,

    /** Local variable declaration */
    LOCAL_VARIABLE,

    /** Annotation type declaration */
    ANNOTATION_TYPE,

    /** Package declaration */
    PACKAGE,

    /**
     * Type parameter declaration
     *
     * @since 1.8
     */
    TYPE_PARAMETER,

    /**
     * Use of a type
     *
     * @since 1.8
     */
    TYPE_USE
}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

// 自定义作用在Field上的注解
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface TestField
{
    String name();
}

// 自定义在method上的注解
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface TestAnnotation
{
    String name();
    int age() default 18;
    int[] score();
}

// 测试类

public class Test
{
    @TestAnnotation(name = "james", age =18 , score = {23,24})
    public void hello(){
        System.out.println("");
    }

    @TestField(name = "james")
    private String username;

    public static void main(String[] args) throws NoSuchMethodException, NoSuchFieldException 
    {
        // 通过反射来回去method 和 fields
        Method method = Test.class.getMethod("hello", null);
        Field[] fields = Test.class.getDeclaredFields();

        for (Field field: fields) {
            if (field.isAnnotationPresent(TestField.class)) {
                TestField annotation = field.getAnnotation(TestField.class);
                System.out.println("annotation.name() = " + annotation.name());
            }
        }
        if(method.isAnnotationPresent(TestAnnotation.class)){
            TestAnnotation tf =  method.getAnnotation(TestAnnotation.class);
            System.out.println("name: " + tf.name() +" age: "+ tf.age());
        }
    }
}

// 输出结果
annotation.name() = james
name: james age: 18