Java学习（11）—— 枚举类

一.   枚举类

       当类的对象是有限个，且是确定的，该类可以称为枚举类； 当需要定义一组常量时，建议使用枚举类；

        1. 自定义枚举类

          （1）定义属性，类中的属性用private final修饰

          （2）私有化类的构造器

          （3）提供当前枚举类的多个对象，声明为public static final

public class Test{
    public static void main(String[] args) {
        Season spring = Season.SPRING;
        System.out.println(spring.toString());  //Season{seasonName='Spring', seasonIntroduction='warm'}
    }
}


class Season{
    private final String seasonName;
    private final String seasonIntroduction;

    private Season(String seasonName, String seasonIntroduction){
        this.seasonName = seasonName;
        this.seasonIntroduction = seasonIntroduction;
    }

    public static final Season SPRING = new Season("Spring","warm");
    public static final Season SUMMER = new Season("Summer","hot");
    public static final Season AUTUMN = new Season("Autumn","cool");
    public static final Season WINTER = new Season("Winter","cold");


    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonIntroduction() {
        return seasonIntroduction;
    }

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

        2. 使用enum关键字定义枚举类

          （1）提供当前枚举类的对象，多个对象之间用逗号隔开，最后一个对象用分号结束

          （2）定义属性，类中的属性用private final修饰

          （3）私有化类的构造器

public class Test{
    public static void main(String[] args) {
        Season spring = Season.SPRING;
        System.out.println(spring.toString());  //SPRING
    }
}


enum Season{
    SPRING("Spring","warm"),
    SUMMER("Summer","hot"),
    AUTUMN("Autumn","cool"),
    WINTER("Winter","cold");

    private final String seasonName;
    private final String seasonIntroduction;

    private Season(String seasonName, String seasonIntroduction){
        this.seasonName = seasonName;
        this.seasonIntroduction = seasonIntroduction;
    }

    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonIntroduction() {
        return seasonIntroduction;
    }
}

       使用enum关键字定义的枚举类自动继承于Enum类

        Enum类中的常用方法 ：

        （1）values()：返回枚举类型的对象数组

        （2）valueOf(String objName)：返回枚举类中对象名是objName的对象，如果没有对象名是objName的枚举类对象，则会抛异常IllegalArgumentException

        （3）toString()：返回当前枚举类对象常量的名称

import java.util.Arrays;

public class Test{
    public static void main(String[] args) {
        Season spring = Season.SPRING;

        System.out.println(spring.toString());         //SPRING

        Season[] season = Season.values();
        System.out.println(Arrays.toString(season));   //[SPRING, SUMMER, AUTUMN, WINTER]

        Season summer = Season.valueOf("SUMMER");
        System.out.println(summer);                    //SUMMER

    }
}


enum Season{
    SPRING("Spring","warm"),
    SUMMER("Summer","hot"),
    AUTUMN("Autumn","cool"),
    WINTER("Winter","cold");

    private final String seasonName;
    private final String seasonIntroduction;

    private Season(String seasonName, String seasonIntroduction){
        this.seasonName = seasonName;
        this.seasonIntroduction = seasonIntroduction;
    }

    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonIntroduction() {
        return seasonIntroduction;
    }
}

        使用enum关键字定义的枚举类来实现接口

       （1）在enum类中实现接口

public class Test{
    public static void main(String[] args) {
        Season spring = Season.SPRING;
        spring.show();    //这是关于季节的枚举类

        Season summer = Season.SUMMER;
        summer.show();    //这是关于季节的枚举类
    }
}

interface Information{
    public void show();
}

enum Season implements Information{
    SPRING("Spring","warm"),
    SUMMER("Summer","hot"),
    AUTUMN("Autumn","cool"),
    WINTER("Winter","cold");

    private final String seasonName;
    private final String seasonIntroduction;

    private Season(String seasonName, String seasonIntroduction){
        this.seasonName = seasonName;
        this.seasonIntroduction = seasonIntroduction;
    }

    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonIntroduction() {
        return seasonIntroduction;
    }

    @Override
    public void show() {
        System.out.println("这是关于季节的枚举类");
    }
}

        （2）让枚举类的对象分别实现接口

public class Test{
    public static void main(String[] args) {
        Season spring = Season.SPRING;
        spring.show();    //春天

        Season summer = Season.SUMMER;
        summer.show();    //夏天
    }
}

interface Information{
    public void show();
}

enum Season implements Information{
    SPRING("Spring","warm"){
        @Override
        public void show() {
            System.out.println("春天");
        }
    },
    SUMMER("Summer","hot"){
        @Override
        public void show() {
            System.out.println("夏天");
        }
    },
    AUTUMN("Autumn","cool"){
        @Override
        public void show() {
            System.out.println("秋天");
        }
    },
    WINTER("Winter","cold"){
        @Override
        public void show() {
            System.out.println("冬天");
        }
    };

    private final String seasonName;
    private final String seasonIntroduction;

    private Season(String seasonName, String seasonIntroduction){
        this.seasonName = seasonName;
        this.seasonIntroduction = seasonIntroduction;
    }

    public String getSeasonName() {
        return seasonName;
    }

    public String getSeasonIntroduction() {
        return seasonIntroduction;
    }

}