Java8新特性之重复注解与类型注解详解

目录

• Java8新特性重复注解与类型注解

• 一、JDK5中的注解

• 1.注解（@）
• 2.作用
• 3.如何理解注解？
• 4.关于注解
• 5.注解分为三个阶段
• 6.注解的属性类型
• 7.为注解增加属性

• 1.类型注解
• 2.重复注解

@SuppressWarnings("deprecation")  //编译器警告过时（source阶段）
@Deprecated      //过时（Runtime阶段）
@Override      //重写（source阶段）
@Retention(RetentionPolicy.RUNTIME) 
//保留注解到程序运行时。（Runtime阶段）
@Target({ElementType.METHOD,ElementType.TYPE})
//标记既能定义在方法上，又能定义在类、接口、枚举上等。

@SuppressWarnings("deprecation")

String value() default "blue"; //定义在注解类中

int[] arrayArr() default {3,4,5,5};//定义在注解类中
SunAnnotation(arrayArr={3,9,8}) //设置数组值

SunAnnotation(arrayArr=9)

EnumDemo.TrafficLamp lamp()

default EnumDemo.TrafficLamp.RED;

MetaAnnotation annotationAttr()
//定义在一个注解类中,并指定缺省值，
//此属性关联到注解类：MetaAnnotation.java, 
default @MetaAnnotation("lhm");
//设置注解属性值
@SunAnnotation(annotationAttr=@MetaAnnotation("flx"))

new @Interned MyObject();

myString = (@NonNull String) str;

class UnmodifiableList<T> implements@Readonly List<@Readonly T> { ... }

void monitorTemperature() throws@Critical TemperatureException { ... }

@Target({ElementType.TYPE_PARAMETER, ElementType.TYPE_USE})
@interface MyAnnotation {}

import checkers.nullness.quals.*;
public class TestDemo{
    void sample() {
        @NonNull Object my = new Object();
    }
}

javac -processor checkers.nullness.NullnessChecker TestDemo.java

@NonNull Object my = null;

import checkers.nullness.quals.*;
public class TestDemo{
    void sample() {
        /*@NonNull*/ Object my = null;
    }
}

@interface MyHints {
    Hint[] value();
}
@Repeatable(MyHints.class)
@interface Hint {
    String value();
}

@MyHints({@Hint("hint1"), @Hint("hint2")})
class Person {}

@Hint("hint1")
@Hint("hint2")
class Person {}

public class RepeatingAnnotations {
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Filters {
        Filter[] value();
    }
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Repeatable(Filters.class)
    public @interface Filter {
        String value();
    }
    @Filter("filter1")
    @Filter("filter2")
    public interface Filterable {
    }
    public static void main(String[] args) {
        for (Filter filter : Filterable.class.getAnnotationsByType(Filter.class)) {
            System.out.println(filter.value());
        }
    }
}

public @interface MyAnnotation {  
     String role();  
}  
public @interface Annotations {  
    MyAnnotation[] value();  
}  
public class RepeatAnnotationUseOldVersion {  
    @Annotations({@MyAnnotation(role="Admin"),@MyAnnotation(role="Manager")})  
    public void doSomeThing(){  
    }  
}

@Repeatable(Annotations.class) 
public @interface MyAnnotation {  
     String role();  
}  
public @interface Annotations {  
    MyAnnotation[] value();  
}  
public class RepeatAnnotationUseOldVersion {  
 @MyAnnotation(role="Admin")  
    @MyAnnotation(role="Manager")
    public void doSomeThing(){  
    }  
} 

package io.mykit.binghe.java8.annotition;
import java.lang.annotation.*;
/**
 * @author binghe
 * @version 1.0.0
 * @description 定义注解
 */
@Repeatable(BingheAnnotations.class)
@Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.CONSTRUCTOR, ElementType.LOCAL_VARIABLE,ElementType.TYPE_PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface BingheAnnotation {
    String value();
}

package io.mykit.binghe.java8.annotation;
import java.lang.annotation.*;
/**
 * @author binghe
 * @version 1.0.0
 * @description 定义注解
 */
@Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.CONSTRUCTOR, ElementType.LOCAL_VARIABLE,ElementType.TYPE_PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface BingheAnnotations {
    BingheAnnotation[] value();
}

package io.mykit.binghe.java8.annotation;
/**
 * @author binghe
 * @version 1.0.0
 * @description 测试注解
 */
@BingheAnnotation("binghe")
@BingheAnnotation("class")
public class Binghe {
    @BingheAnnotation("init")
    @BingheAnnotation("method")
    public void init(){
    }
}

package io.mykit.binghe.java8.annotation;
import java.lang.reflect.Method;
import java.util.Arrays;
/**
 * @author binghe
 * @version 1.0.0
 * @description 测试注解
 */
public class BingheAnnotationTest {
    public static void main(String[] args) throws NoSuchMethodException {
        Class<Binghe> clazz = Binghe.class;
        BingheAnnotation[] annotations = clazz.getAnnotationsByType(BingheAnnotation.class);
        System.out.println("类上的重复注解如下：");
        Arrays.stream(annotations).forEach((a) -> System.out.print(a.value() + " "));
        System.out.println();
        System.out.println("=============================");
        Method method = clazz.getMethod("init");
        annotations = method.getAnnotationsByType(BingheAnnotation.class);
        System.out.println("方法上的重复注解如下：");
        Arrays.stream(annotations).forEach((a) -> System.out.print(a.value() + " "));
    }
}

类上的重复注解如下：
binghe class 
=============================
方法上的重复注解如下：
init method