Annotation

2019-08-09 00:00:00 Annotation

   在进行类或方法定义的时候,都可以使用一系列的Annotation(public interface Annotation)进行声明,如果想要获取这些Annotation的信息,可以直接通过反射来完成。在 java.lang.reflect 里面有一个AccessibleObject类,在本类中提供有Annotation类的方法:

  1.获取全部Annotation:public Annotation[] getAnnotations();

  2.获取指定Annotation:public <T extends Annotation> T getAnnotation​(Class<T> annotationClass)

 

package com.annotation.demo;

import java.io.Serializable;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;

@FunctionalInterface
@Deprecated(forRemoval = false,since = "1.1")
interface IMessage{
    public void send(String msg);
}

@SuppressWarnings("serial")
class MessageImpl implements IMessage,Serializable{
    @Override
    @Deprecated(since = "1.3")
    public void send(String msg) {
        System.out.println("【消息发送】" + msg);
    }
}

public class annotationdemo {
    public static void main(String[] args) throws Exception {
        {
            System.out.println("-----------------------IMessage接口:-----------------------------");
            Annotation annotations[] = IMessage.class.getAnnotations();//获取接口上的全部Annotation
            for(Annotation annotation:annotations){
                System.out.println(annotation);
            }
        }
        
        {
            System.out.println("-----------------------MessageImpl子类:-----------------------------");
            Annotation annotations[] = MessageImpl.class.getAnnotations();//获取MessageImpl子类上的全部Annotation
            for(Annotation annotation:annotations){
                System.out.println(annotation);
            }
        }

        {
            System.out.println("-----------------------send()方法:-----------------------------");
            Method method = MessageImpl.class.getDeclaredMethod("send", String.class);
            Annotation annotations[] = method.getAnnotations();//获取send方法上的全部Annotation
            for(Annotation annotation:annotations){
                System.out.println(annotation);
            }
        }
    }
}

 

不同的Annotation有不同的作用范围:

Annotation名称作用范围                          
@SuppressWarnings
 

@Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE, MODULE})

@Retention(RetentionPolicy.SOURCE)

public @interface SuppressWarnings {}

@FunctionalInterface

@Documented

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.TYPE)

public @interface FunctionalInterface {}

@Deprecated
 @Documented

@Retention(RetentionPolicy.RUNTIME)

@Target(value={CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, MODULE, PARAMETER, TYPE})

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