Java，get与getDeclared的区别，@Inherited的作用

超、凢脫俗 2022-12-26 08:10 110阅读 0赞

看以下实例，实例中有注释说明

import java.lang.annotation.*;
    
    /**
    * Title: SuperClassDBTable
    * Description:
    * @date 2018/1/26 15:27
    */
    @Inherited
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface SuperClassDBTable {
        public String name() default "";
    }

import java.lang.annotation.*;
    
    /**
    * Title: SuperDBTable
    * Description:
    * @date 2018/1/26 15:06
    */
    @Inherited
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface SuperDBTable {
        public String name() default "";
    }

import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
     
    /**
     * Title: SubDBTable
     * Description:
     * @date 2018/1/26 15:22
     */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface SubDBTable {
    
    }

import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
    * Title: SubAnnotation
    * @date 2018/2/10 14:07
    */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface SubAnnotation {
    
    }

@SuperClassDBTable(name = "SuperClassDBTable")
    class SuperClass {
        private int superSuperPrivateF;
        public int superSuperPublicF;
     
        public SuperClass() {  }
     
        private int superSuperPrivateM() {
            return 0;
        }
     
        public int superSuperPubliceM() {
            return 0;
        }
    }

@SuperDBTable(name = "SuperDBTable")
    class Super extends SuperClass {
        private int superPrivateF;
        public int superPublicF;
     
        public Super() { }
     
        private int superPrivateM() {
            return 0;
        }
     
        public int superPubliceM() {
            return 0;
        }
    }

@SubDBTable
    @SubAnnotation
    class Sub extends Super {
        private int subPrivateF;
        public int subPublicF;
     
        private Sub() { }
     
        public Sub(int i) {
        }
     
        private int subPrivateM() {
            return 0;
        }
     
        public int subPubliceM() {
            return 0;
        }
    }

import java.util.Arrays;
     
    /**
     * 1.演示从Class对象上获得反射元素Field Method Constructor
     * 2.演示注解@Inherited的作用
     *
     */
    public class Main {
        public static void main(String[] args) {
            Class<Sub> clazz = Sub.class;
            System.out.println("======Field=====");
            //自身public + 继承public
            System.out.println(Arrays.toString(clazz.getFields()));
    //输出结果:[public int Sub.subPublicF, public int Super.superPublicF, public int SuperClass.superSuperPublicF]
            //自身所有
            System.out.println(Arrays.toString(clazz.getDeclaredFields()));
     //输出结果:[private int Sub.subPrivateF, public int Sub.subPublicF]
            System.out.println("==========Method=========");
            //自身public + 继承public
            System.out.println(Arrays.toString(clazz.getMethods()));
    //输出结果:[public int Sub.subPubliceM(), public int Super.superPubliceM(), public int SuperClass.superSuperPubliceM(), public final void java.lang.Object.wait() throws java.lang.InterruptedException, public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException, public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException, public boolean java.lang.Object.equals(java.lang.Object), public java.lang.String java.lang.Object.toString(), public native int java.lang.Object.hashCode(), public final native java.lang.Class java.lang.Object.getClass(), public final native void java.lang.Object.notify(), public final native void java.lang.Object.notifyAll()]
            //自身所有
            System.out.println(Arrays.toString(clazz.getDeclaredMethods()));
    //输出结果:[private int Sub.subPrivateM(), public int Sub.subPubliceM()]
     
            System.out.println("=======Constructor=======");
            //自身public构造函数
            System.out.println(Arrays.toString(clazz.getConstructors()));
    //输出结果:[public Sub(int)]
            //自身所有构造函数
            System.out.println(Arrays.toString(clazz.getDeclaredConstructors()));
    //输出结果:[private Sub(), public Sub(int)]
     
            System.out.println("========AnnotatedElement========");
            //如果该类存在指定注解SubDBTable，则返回true，反之返回false
            System.out.println(clazz.isAnnotationPresent(SubDBTable.class));//这里的SubDBTable是注解，不是类。以下同是注解。
    //输出结果:true
            //如果该类存在指定注解SubDBTable，则返回该注释，反之返回null。
            System.out.println(clazz.getAnnotation(SubDBTable.class));
    //输出结果:@SubDBTable()
            //如果该类存在指定注解SubAnnotation，则返回true，反之返回false
            System.out.println(clazz.isAnnotationPresent(SubAnnotation.class));
    //输出结果:true
            //如果该类存在指定注解SubAnnotation，则返回该注释，反之返回null。
            System.out.println(clazz.getAnnotation(SubAnnotation.class));
    //输出结果:@SubAnnotation()
            //自身注解+继承注解
            System.out.println(Arrays.toString(clazz.getAnnotations()));
    //输出结果:[@SuperClassDBTable(name=SuperClassDBTable), @SuperDBTable(name=SuperDBTable), @SubDBTable(), @SubAnnotation()]
            //自身注解
            System.out.println(Arrays.toString(clazz.getDeclaredAnnotations()));
    //输出结果:[@SubDBTable(), @SubAnnotation()]
        }
    }
     
    //如果SuperClassDBTable的元注解中没有@Inherited，则
    System.out.println(Arrays.toString(clazz.getAnnotations()));
    //输出结果:[@SuperDBTable(name=SuperDBTable), @SubDBTable(), @SubAnnotation()]
    //如果SuperDBTable的元注解中没有@Inherited，则
    System.out.println(Arrays.toString(clazz.getAnnotations()));
    //输出结果:[@SuperClassDBTable(name=SuperClassDBTable), @SubDBTable(), @SubAnnotation()] //中间的继承关系没有断掉
    //如果SuperClassDBTable的元注解中没有@Inherited，SuperDBTable的元注解中没有@Inherited，则
    System.out.println(Arrays.toString(clazz.getAnnotations()));
    //输出结果:[@SubDBTable(), @SubAnnotation()]