java 注解 @Override

一 笔记

@Override 专门给编译器参考的；带有Override编译器在编译时都会进行检查；检查这个方法是否重写了父类的方法，

• 如果不是重写了父类的方法，编译器会自动报错；
• 注解的作用：1、做编译检查的；2、被反射机制解析；
• @Override 只能标注方法，不能标注类；

二 Override源码

/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang;

import java.lang.annotation.*;

/**
 * Indicates that a method declaration is intended to override a
 * method declaration in a supertype. If a method is annotated with
 * this annotation type compilers are required to generate an error
 * message unless at least one of the following conditions hold:
 *
 * 

 * The method does override or implement a method declared in a
 * supertype.
 * 

 * The method has a signature that is override-equivalent to that of
 * any public method declared in {@linkplain Object}.
 * 
 *
 * @author  Peter von der Ahé
 * @author  Joshua Bloch
 * @jls 9.6.1.4 @Override
 * @since 1.5
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.SOURCE)
public @interface Override {
}

三 使用@Override注解

public class AnnotationTest02 extends Object{
//    检查是否有重写父类的方法；检查到没有重写，就会报编译错误；
    @Override
    public String toString(){
        return "AnnotationTest02";
    }
}