java枚举类

一、 枚举类的说明

枚举类的理解：类的对象只有有限个，确定的。
当需要定义一组常量时，强烈建议使用枚举类
如果枚举类只一个对象，则可以作为单例模式的实现方式。

二、如何定义枚举类

① 自定义枚举类

class Season{
    // 1.声明Season对象的属性：private final修饰
    private final String seasonName;
    private final String seasonDesc;

    // 私有化的构造器，并给对象赋值
    private Season(String seasonName, String seasonDesc){
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }

    // 3.提供当前枚举类的多个对象：public static final的
    public static final Season SPRING = new Season("春天","春暖花开");
    public static final Season SUMMER = new Season("夏天","夏日炎炎");
    public static final Season AUTUMN = new Season("秋天","秋高气爽");
    public static final Season WINTER = new Season("冬天","冰天雪地");

    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }

    @Override
    public String toString() {
        return "Season{" +
                "seasonName='" + seasonName + '\'' +
                ", seasonDesc='" + seasonDesc + '\'' +
                '}';
    }
}

public class SeasonTest {
    public static void main(String[] args) {
        Season autumn = Season.AUTUMN;
        System.out.println(autumn); // Season{seasonName='秋天', seasonDesc='秋高气爽'}
    }
}

② JDK5.0 新增使用 enum 定义枚举类。

// 使用enum关键枚举类
enum Season1{
    // 1.提供当前枚举类的对象，多个对象之间用“,”隔开，末尾对象";"结束
    SPRING("春天","春暖花开"),
    SUMMER("夏天","夏日炎炎"),
    AUTUMN("秋天","秋高气爽"),
    WINTER("冬天","冰天雪地");

    // 2.声明Season对象的属性：private final修饰
    private final String SeasonName;
    private final String SeasonDesc;

    // 3.私有化构造器，并给对象赋值
    private Season1(String SeasonName, String SeasonDesc){
        this.SeasonName = SeasonName;
        this.SeasonDesc = SeasonDesc;
    }
    // 4.获取枚举类对象的属性

    public String getSeasonName() {
        return SeasonName;
    }

    public String getSeasonDesc() {
        return SeasonDesc;
    }

    @Override
    public String toString() {
        return "Season1{" +
                "SeasonName='" + SeasonName + '\'' +
                ", SeasonDesc='" + SeasonDesc + '\'' +
                '}';
    }
}

public class SeasonTest2 {
    public static void main(String[] args) {
        Season1 season = Season1.AUTUMN;
        System.out.println(season); // Season1{SeasonName='秋天', SeasonDesc='秋高气爽'}
    }

}

③ emum 定义枚举类之后，枚举类常用方法：（继承于 java.lang.Enum 类）

• value() 返回所有的枚举类对象的构成的数组
• valueOf(String objName):返回枚举类中对象名是 objName 的对象。

interface Info{
    void show();
}

// 使用enum关键字枚举类
enum Season2 implements Info{
    //1.提供当前枚举类的对象，多个对象之间用","隔开，末尾对象";"结束
    SPRING("春天","春暖花开"){
        @Override
        public void show() {
            System.out.println("春天在那里");
        }
    },
    SUMMER("夏天","夏日炎炎"){
        @Override
        public void show() {
            System.out.println("宁夏");
        }
    },
    AUTUMN("秋天","秋高气爽"){
        @Override
        public void show() {
            System.out.println("秋天不回来");
        }
    },
    WINTER("冬天","冰天雪地"){
        @Override
        public void show() {
            System.out.println("大约在冬季");
        };
    };
    private final String SeasonName;
    private final String SeasonDesc;

    private Season2(String SeasonName , String SeasonDesc){
        this.SeasonName = SeasonName;
        this.SeasonDesc = SeasonDesc;
    }

    public String getSeasonName() {
        return SeasonName;
    }

    public String getSeasonDesc() {
        return SeasonDesc;
    }

    @Override
    public String toString() {
        return "Season2{" +
                "SeasonName='" + SeasonName + '\'' +
                ", SeasonDesc='" + SeasonDesc + '\'' +
                '}';
    }
}

public class SeasonTest3 {
    public static void main(String[] args) {
        Season2 season = Season2.AUTUMN;
        System.out.println(season.toString()); //Season2{SeasonName='秋天', SeasonDesc='秋高气爽'}
        season.show(); // 秋天不回来

        // value 返回所有的枚举类对象的构成的数组
        Season2[] values = season.values();
//        for (Season2 value : values) {
//            System.out.println(value);
//            value.show();
//        }
        for(int i = 0 ; i <values.length; i++){
            System.out.println(values[i]);
            values[i].show();
        }
        System.out.println("*************************************************");

        Thread.State[] values1 = Thread.State.values();
        for(int i = 0 ; i < values1.length; i++){
            System.out.println(values1[i]);
        }
        System.out.println("***************************************");
        // valueOf(String objName):返回枚举类中对象名是objName的对象。
        Season2 spring = Season2.valueOf("SPRING");
        System.out.println(spring); // Season2{SeasonName='春天', SeasonDesc='春暖花开'}
    }

运行结果：

• value（）