java8 新增的@Repeatable注解

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{                            }        }