枚举类与注解

枚举类与注解

类的对象只有有限个，确定的

当需要定义一组常量时，推荐枚举类

如果枚举类中只有一个对象，则可以作为单例模式的实现方式

*如何自定义枚举类

方式一： jdk 1.5 之前，自定义枚举类

package SeaTest;
//自定义一个枚举类
public class SeasonTest {

    public static void main(String[] args) {
        final Season spring = Season.SPRING;
        System.out.println(spring);

        Season season=new Season("1","2");
        System.out.println(season);
    }

    //自定义枚举类
    static class Season{
        //1.声明 seanson 对象 属性
        private final String seasonName;
        private final String seaonDesc;
        //2.私有化构造器，给对象赋值
        private Season(String seasonName,String seaonDesc){
            this.seasonName=seasonName;
            this.seaonDesc=seaonDesc;
        }
        //3.提供当前 枚举类的 多个对象

        public static final Season SPRING =new Season("春天","春1");
        public static final Season SUMMER =new Season("夏天","春2");
        public static final Season FULL   =new Season("秋天","春3");
        public static final Season WINTER =new Season("冬天","春4");
        //4.其他诉求 ： 获取 枚举类对象的属性

        public String getSeasonName() {
            return seasonName;
        }

        public String getSeaonDesc() {
            return seaonDesc;
        }

        @Override
        public String toString() {
            return "Season{" +
                    "seasonName='" + seasonName + ''' +
                    ", seaonDesc='" + seaonDesc + ''' +
                    '}';
        }
    }
}
Season{seasonName='春天', seaonDesc='春1'}
Season{seasonName='1', seaonDesc='2'}

方式二 : jdk 5.0 之后，使用关键字 enum 定义枚举类

package SeaTest;
//自定义一个枚举类
public class SeasonTest2 {

    public static void main(String[] args) {
        final Season full = Season.FULL;
        System.out.println(full);

        //定义枚举类 默认 继承于 class java.lang.Enum
        System.out.println(full.getClass().getSuperclass());
    }

    //使用关键字 enum定义枚举类
    enum  Season{
        //1.提供当前枚举类对象，多个对象之间用 “,”隔开，“；”结尾 置顶
         SPRING ("春天","春1"),
         SUMMER ("夏天","春2"),
         FULL   ("秋天","春3"),
         WINTER ("冬天","春4");



        //1.声明 seanson 对象 属性
        private final String seasonName;
        private final String seaonDesc;
        //2.私有化构造器，给对象赋值
        private Season(String seasonName,String seaonDesc){
            this.seasonName=seasonName;
            this.seaonDesc=seaonDesc;
        }
        //3.提供当前 枚举类的 多个对象


        //4.其他诉求 ： 获取 枚举类对象的属性

        public String getSeasonName() {
            return seasonName;
        }

        public String getSeaonDesc() {
            return seaonDesc;
        }

        @Override
        public String toString() {
            return "Season{" +
                    "seasonName='" + seasonName + ''' +
                    ", seaonDesc='" + seaonDesc + ''' +
                    '}';
        }
    }
}
Season{seasonName='秋天', seaonDesc='春3'}
class java.lang.Enum

** emun类中的常用方法

package SeaTest;
//自定义一个枚举类
public class SeasonTest2 {

    public static void main(String[] args) {
        final Season1 full = Season1.FULL;
        System.out.println(full);
        System.out.println("----------------------");
        //定义枚举类 默认 继承于 class java.lang.Enum
        System.out.println(full.getClass().getSuperclass());
        System.out.println("----------------------");
        Season1 full1 = Season1.valueOf("FULL");
        System.out.println(full1);
        System.out.println("----------------------");
        final Season1[] values = Season1.values();
        for (Season1 value : values) {
            System.out.println(value);
        }
    }

    //使用关键字 enum定义枚举类
    enum  Season1{
        //1.提供当前枚举类对象，多个对象之间用 “,”隔开，“；”结尾 置顶
         SPRING ("春天","春1"),
         SUMMER ("夏天","春2"),
         FULL   ("秋天","春3"),
         WINTER ("冬天","春4");



        //1.声明 seanson 对象 属性
        private final String seasonName;
        private final String seaonDesc;
        //2.私有化构造器，给对象赋值
        private Season1(String seasonName,String seaonDesc){
            this.seasonName=seasonName;
            this.seaonDesc=seaonDesc;
        }
        //3.提供当前 枚举类的 多个对象


        //4.其他诉求 ： 获取 枚举类对象的属性

        public String getSeasonName() {
            return seasonName;
        }

        public String getSeaonDesc() {
            return seaonDesc;
        }

        @Override
        public String toString() {
            return "Season{" +
                    "seasonName='" + seasonName + ''' +
                    ", seaonDesc='" + seaonDesc + ''' +
                    '}';
        }
    }
}
Season{seasonName='秋天', seaonDesc='春3'}
----------------------
class java.lang.Enum
----------------------
Season{seasonName='秋天', seaonDesc='春3'}
----------------------
Season{seasonName='春天', seaonDesc='春1'}
Season{seasonName='夏天', seaonDesc='春2'}
Season{seasonName='秋天', seaonDesc='春3'}
Season{seasonName='冬天', seaonDesc='春4'}

Process finished with exit code 0

枚举类实现接口

** 注解

自定义注解

关键字 @interface

1. 注解声明 @interface
1. 内部定义成员，通常是 value 表示
1. 可以指定成员的默认值，使用 default 定义
1. 如果自定义注解没有成员，表明是一个标识作用
1. 如果注解有成员，在使用时，需要指明成员的值
1. 自定义注解必须配上注解的信息处理流程（使用反射）
7.通常会指明 @Retention @Target

package SeaTest;

public @interface MyAnnotation {

    String[] value() default "hi";
}
@MyAnnotation(value = "dy")
class Test{

}

JDK 5 提供的元注解

元注解 : 对现有的注解进行解释说明

jdk8 中注解的新特性：可重复注解类型注解

枚举类与注解

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