36 枚举类

枚举类

​ 类的对象只有有限个，确定的。举例如下：

星期:Monday(星期一)...Sunday(星期天

性别：Man(男)、Woman(女)

就职状态:Busy、Free、Vocation、Dimission

当需要定义一组常量时，强烈建议使用枚举类

如何定义枚举类

方式一：jdk5.0之前，自定义枚举类

public class SeasonTest {
    public static void main(String[] args) {
        Season autumn = Season.AUTUMN;
        System.out.println(autumn);//要重写tuString()方法，不然只是地址
    }

}

//自定义枚举类
class Season{
    //1.声明Season对象的属性:需要private、final属性修饰
    private final String seasonName ;
    private final String seasonDesc;


    //2.私有化类的构造器
    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("秋天","秋高气爽");
    public static final Season AUTUMN = new Season("夏天","夏日炎炎");
    public static final Season WINTER = new Season("冬天","冰天雪地");

    //4.其他诉求：获取枚举类对象的属性
    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }

    //5.其他诉求1：提供toString（）

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

方式二：jdk5.0，可以使用enum关键字定义枚举类

说明：定义的枚举类默认继承于java.lang.Enum类

public class SeasonTest1 {
    public static void main(String[] args) {
        Season1 summer = Season1.SUMMER;
        System.out.println(summer);
    }
}
//用enum关键字枚举类
public enum Season1{
    //1.当前枚举类的对象，多个对象之间用“，”隔开，末尾对象用“；”结束，且必须在最上面
    SPRING("春天","春暖花开"),
    SUMMER("秋天","秋高气爽"),
    AUTUMN("夏天","夏日炎炎"),
     Season1("冬天","冰天雪地");

    //2.声明Season对象的属性:需要private、final属性修饰
    private final String seasonName ;
    private final String seasonDesc;


    //3.私有化类的构造器
    private Season1(String seasonName,String seasonDesc){
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }

    //4.其他诉求：获取枚举类对象的属性
    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }

    //5.其他诉求1：提供toString（）

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

Enum类中的常用方法

values()方法:返回枚举类型的对象数组。该方法可以很方便地遍历所有的枚举值

        Season1[] values = Season1.values();
        for(int i = 0;i < values.length;i++){
            System.out.println(values[i]);
        }

返回枚举类中对象名是str的对象

valueof(String str):可以把一个字符串转为对应的枚举类对象。要求字符串必须是枚举类对象的“名字”。如不是，会有运行时异常:
llegalArgumentException。
toString():返回当前枚举类对象常量的名称

使用enum关键字定义的枚举类实现接口的情况

情况一：实现接口，在enum类中实现抽象方法

情况二：让枚举类的对象分别实现接口中的抽象方法

public class SeasonTest1 {
    public static void main(String[] args) {
        Season1 summer = Season1.SUMMER;
        System.out.println(summer);

        Season1[] values = Season1.values();
        for(int i = 0;i < values.length;i++){
            System.out.println(values[i]);
        }
        summer.show();
    }
}

interface Info{
    void show();
}

//用enum关键字枚举类
enum Season1 implements Info{
    //1.当前枚举类的对象，多个对象之间用“，”隔开，末尾对象用“；”结束
    SPRING("春天","春暖花开"){
        @Override
        public void show() {
            System.out.println("春天在哪里");
        }
    },
    SUMMER("秋天","秋高气爽"){
        @Override
        public void show() {
            System.out.println("秋天");
        }
    },
    AUTUMN("夏天","夏日炎炎"){
        @Override
        public void show() {
            System.out.println("夏天夏天悄悄过去");
        }
    },
    WINTER("冬天","冰天雪地"){
        @Override
        public void show() {
            System.out.println("大约在冬季");
        }
    };


    //2.声明Season对象的属性:需要private、final属性修饰
    private final String seasonName ;
    private final String seasonDesc;


    //3.私有化类的构造器
    private Season1(String seasonName,String seasonDesc){
        this.seasonName = seasonName;
        this.seasonDesc = seasonDesc;
    }

    //4.其他诉求：获取枚举类对象的属性
    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonDesc() {
        return seasonDesc;
    }

    //5.其他诉求1：提供toString（）

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

//    @Override
//    public void show() {
//        System.out.println("这是个季节");
//    }
}