【Java】枚举类

1.枚举类

• 类的对象只有有限个，对象是确定的。
• 当需要定义一组常量时，强烈建议使用枚举类。
• 如果枚举类中只有一个对象，则可以作为单例模式的实现方式。

2.定义枚举类

• JDK 5.0之前：自定义枚举类
• JDK 5.0之后：使用enum关键字定义

（1）自定义枚举类

public class Season {
    //1.对象属性private final修饰
    private final String seasonName;
    private final String seasonDesc;

    //2.私有构造器
    private Season(String seasonName,String seasonDesc){
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }

    //3.当前枚举类的多个对象，public static final修饰
    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 + '\'' +
                '}';
    }
}

调用时直接通过类名.对象
System.out.println(Season.SPRING);

（2）使用enum

• 所有对象要写在开头，否则会报错。
• 对象之间用逗号隔开，结尾用分号。
• 定义的枚举类默认继承于java.lang.Enum类

enum Season {
    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");

    private final String seasonName;
    private final String seasonDesc;

    private Season(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 "Season{" +
                "seasonName='" + seasonName + '\'' +
                ", seasonDesc='" + seasonDesc + '\'' +
                '}';
    }
}

常用方法

	System.out.println(Season2.SUMMER); //调用方式
        System.out.println(Season2.valueOf("WINTER")); //返回指定对象名的对象

        Season2[] seasons = Season2.values();          //返回所有的枚举类对象构成的数组
        for (int i = 0; i < seasons.length; i++) {
            System.out.println(seasons[i]);
        }

        Thread.State[] states = Thread.State.values(); //返回所有线程状态
        for (int i = 0; i < states.length; i++) {
            System.out.println(states[i]);
        }