获取方法标注少

注释不与原代码的操作干扰。在标志中发挥作用。注释工具允许第三方募集

记笔记，要完成所需的任务。

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 = "", tenum = {TestEnum.TEST1})
<span style="white-space:pre">	</span>public User getUser(User user) {
<span style="white-space:pre">		</span>return user;
<span style="white-space:pre">	</span>}


}

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。由于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 字节码中有注解可是不载入到虚拟机。RUNTIME能够通过反射获取到注解信息，而注解框架也是採用的这样的原理。