重复注解与类型注解

Java8对注解处理提供了两点该进,可重复的注解及可用于类型的注解

重复注解定义使用

新建注解

package com.dance.java8.day01.annotation;import java.lang.annotation.Repeatable;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;import static java.lang.annotation.ElementType.*;import static java.lang.annotation.ElementType.LOCAL_VARIABLE;// 重复注解 必须使用@Repeatable修饰 并指定注解容器@Repeatable(MyAnnotations.class)@Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE})@Retention(RetentionPolicy.RUNTIME)public @interface MyAnnotation {String value() default \"flower\";}

新建注解容器

package com.dance.java8.day01.annotation;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;import static java.lang.annotation.ElementType.*;@Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE})@Retention(RetentionPolicy.RUNTIME)public @interface MyAnnotations {MyAnnotation[] value();}

新建测试类

package com.dance.java8.day01.annotation;import java.lang.reflect.Method;import java.util.Arrays;/*** 重复注解与类型注解*/public class TestAnnotation {public static void main(String[] args) throws NoSuchMethodException {Class<TestAnnotation> testAnnotationClass = TestAnnotation.class;Method show = testAnnotationClass.getMethod(\"show\");Arrays.stream(show.getAnnotationsByType(MyAnnotation.class)).forEach(System.out::println);}@MyAnnotation(\"flower\")@MyAnnotation(\"dance\")public void show(){}}

执行结果

@com.dance.java8.day01.annotation.MyAnnotation(value=flower)@com.dance.java8.day01.annotation.MyAnnotation(value=dance)

类型注解定义使用

修改注解,增加类型注解

package com.dance.java8.day01.annotation;import java.lang.annotation.*;import static java.lang.annotation.ElementType.*;import static java.lang.annotation.ElementType.LOCAL_VARIABLE;// 重复注解 必须使用@Repeatable修饰 并指定注解容器@Repeatable(MyAnnotations.class)@Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE, TYPE_PARAMETER})@Retention(RetentionPolicy.RUNTIME)public @interface MyAnnotation {String value() default \"flower\";}

修改测试类

package com.dance.java8.day01.annotation;import java.lang.annotation.Annotation;import java.lang.reflect.Method;import java.util.Arrays;/*** 重复注解与类型注解*/public class TestAnnotation {public static void main(String[] args) throws NoSuchMethodException {Class<TestAnnotation> testAnnotationClass = TestAnnotation.class;Method show = testAnnotationClass.getMethod(\"show\",String.class);Arrays.stream(show.getAnnotationsByType(MyAnnotation.class)).forEach(System.out::println);Annotation[][] parameterAnnotations = show.getParameterAnnotations();Arrays.stream(parameterAnnotations).forEach(x-> Arrays.stream(x).forEach(System.out::println));}@MyAnnotation(\"flower\")@MyAnnotation(\"dance\")public void show(@MyAnnotation(\"string\") String s){}}

执行结果

@com.dance.java8.day01.annotation.MyAnnotation(value=flower)@com.dance.java8.day01.annotation.MyAnnotation(value=dance)@com.dance.java8.day01.annotation.MyAnnotation(value=string)

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作者：彼岸舞

时间：2021\\12\\13

内容关于：Java

本文属于作者原创,未经允许,禁止转发