注解是不干扰原来的代码的执行的，起到一种标识作用，让第三方的注解工具来提

取注解，来完成所需的任务。

package two.zj;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Documented
@Retention<span style="color:#ff0000;">(</span><span style="background-color: rgb(255, 0, 0);">RetentionPolicy.RUNTIME</span><span style="color:#ff0000;">)</span>
@Target(ElementType.METHOD)
public @interface TestZJ {
	public int id() default 1;
	public String name() default "nametest";
	public String value() ;
	public abstract int [] intt();
	public abstract TestEnum[] tenum();
	
	
}

package two;import two.zj.TestEnum;import two.zj.TestZJ;public class UserAnn {<span style="white-space:pre">	</span>/**<span style="white-space:pre">	</span> * @param user<span style="white-space:pre">	</span> * @return user<span style="white-space:pre">	</span> */<span style="white-space:pre">	</span>@TestZJ(id=22,name="liyy", intt = { 0,1,2,3 }, value = http://www.mamicode.com/"", tenum = {TestEnum.TEST1})>
package two;


import java.lang.reflect.Method;


import two.zj.TestZJ;


public class Testmain {


public static void main(String[] args) throws ClassNotFoundException {
// Class class1 = Class.forName("two.UserAnn");
Class class1 = UserAnn.class;
Method [] methods = class1.getDeclaredMethods();
for(Method method:methods){
TestZJ annotations = method.getAnnotation(TestZJ.class);
if(annotations !=null){
System.out.println(annotations.id());
}
}
}
}
当注解类TestZJ中的@Retention(RetentionPolicy.RUNTIME)   为source 或者class 时候 反射是获取不到注解类的，因为jdk用说明
public enum RetentionPolicy {
    /**
     * 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
}
SOURCE在编译的c字节码中去掉注解，CLASS 字节码中有注解但是不加载到虚拟机，RUNTIME可以通过反射获取到注解信息，而注解框架也是采用的这种原理。

获取不到方法的注解