java8 新增的@Repeatable注解

心已赠人 2021-09-11 06:14 393阅读 0赞

1.  \* java8 新增的@Repeatable注解，其实只是语法糖而已．  
2.   \* java8 注解的 \{ @link RepeatAnn\} 类与 \{ @link Annotations\}是等价的．  
3.   \* 新注解讲语法糖转化为注解值为数组形式．

package com.github.jdk8.ebook.java8_recipes2nd_edition;  
          
        import java.lang.annotation.Annotation;  
        import java.lang.annotation.ElementType;  
        import java.lang.annotation.Repeatable;  
        import java.lang.annotation.Retention;  
        import java.lang.annotation.RetentionPolicy;  
        import java.lang.annotation.Target;  
        import java.util.Arrays;  
          
          
        /** 
         * java8 新增的@Repeatable注解，其实只是语法糖而已． 
         * java8 注解的 {@link RepeatAnn} 类与 {@link Annotations}是等价的． 
         * 新注解讲语法糖转化为注解值为数组形式． 
         * @author doctor 
         * 
         * @since 2015年2月3日 下午8:33:43 
         */  
        public class Chapter2Code {  
          
            public static void main(String[] args) {  
                Annotation[] annotations = RepeatAnn.class.getAnnotations();  
                System.out.println(annotations.length); //1  
                Arrays.stream(annotations).forEach(System.out::println);//@com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Roles(value=[@com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Role(name=doctor), @com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Role(name=who)])  
          
                Annotation[] annotations2 = Annotations.class.getAnnotations();  
                System.out.println(annotations2.length);//1  
                Arrays.stream(annotations2).forEach(System.out::println);//@com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Roles(value=[@com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Role(name=doctor), @com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Role(name=who)])  
                  
            }  
          
            /** 
             * The same annotation can be applied to a declaration or type more than 
             * once, given that each annotation is marked as @Repeatable. In the 
             * following code, the @Repeatable annotation is used to develop an 
             * annotation that can be repeated, rather than grouped together as in 
             * previous releases of Java. In this situation, an annotation named Role is 
             * being created, and it will be used to signify a role for an annotated 
             * class or method. 
             *  
             * @author doctor 
             * 
             * @since 2015年2月3日 下午8:51:09 
             */  
            @Repeatable(value = Roles.class)  
            public static @interface Role {  
                String name() default "doctor";  
            }  
          
            @Target(ElementType.TYPE)  
            @Retention(RetentionPolicy.RUNTIME)  
            public static @interface Roles {  
                Role[] value();  
            }  
              
            @Role(name = "doctor")  
            @Role(name = "who")  
            public static class RepeatAnn{  
                  
            }  
              
            @Roles({@Role(name="doctor"),  
                    @Role(name="who")})  
            public static class Annotations{  
                  
            }  
        }

来自：http://blog.csdn.net/doctor\_who2004/article/details/43457689