枚举类的使用

枚举类的理解：类的对象只有有限个，确定的。我们称此类为枚举类
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。

如何定义枚举类

方式一：jdk5.0之前，自定义枚举类

//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;

class Season{

    //1.声明Season对象的属性:private final修饰

    private final String seasonName;

    private final String seasonDesc;

    //2.私有化类的构造器,并给对象属性赋值

    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");

    //4.其他诉求1：获取枚举类对象的属性

    public String getSeasonName() {

        return seasonName;

    }

    public String getSeasonDesc() {

        return seasonDesc;

    }

    //4.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

使用 enum 定义的枚举类默认继承了 java.lang.Enum类，因此不能再继承其他类

枚举类的构造器只能使用 private 权限修饰符

枚举类的所有实例必须在枚举类中显式列出(, 用于分隔 ; 用于结尾)。列出的实例系统会自动添加 public static final 修饰

必须在枚举类的第一行声明枚举类对象

enum Season1 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"),

    SUMMER("夏天","夏日炎炎"),

    AUTUMN("秋天","秋高气爽"),

    WINTER("冬天","冰天雪地");

//每个枚举对象就相当于调用了其私有的构造器，括号的参数则给Season的属性赋了值

    //2.声明Season对象的属性:private final修饰

    private final String seasonName;

    private final String seasonDesc;

    //2.私有化类的构造器,并给对象属性赋值

    private Season1(String seasonName,String seasonDesc){

        this.seasonName = seasonName;

        this.seasonDesc = seasonDesc;

    }

    //4.其他诉求1：获取枚举类对象的属性

    public String getSeasonName() {

        return seasonName;

    }

    public String getSeasonDesc() {

        return seasonDesc;

    }

//    //4.其他诉求1：提供toString()

//

//    @Override

//    public String toString() {

//        return "Season1{" +

//                "seasonName='" + seasonName + '\'' +

//                ", seasonDesc='" + seasonDesc + '\'' +

//                '}';

//    }

}

Enum类的主要方法

toString()

返回枚举类对象的名称

values()

返回所有的枚举类对象构成的数组

Season1[] values = Season1.values();

        for(int i = 0;i < values.length;i++){

            System.out.println(values[i]);

        }

valueOf(String objName)

返回枚举类中对象名是objName的对象

 Season1 winter = Season1.valueOf("WINTER");

        //如果没有objName的枚举类对象，则抛异常：IllegalArgumentException

//        Season1 winter = Season1.valueOf("WINTER1");

        System.out.println(winter);

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

interface Info{

    void show();

}

enum Season1 implements Info{

    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 Season1(String seasonName,String seasonDesc){

        this.seasonName = seasonName;

        this.seasonDesc = seasonDesc;

    }

    public String getSeasonName() {

        return seasonName;

    }

    public String getSeasonDesc() {

        return seasonDesc;

    }

    @Override

    public void show() {

      System.out.println("这是一个季节");

    }

}

情况二：让枚举类的对象分别实现接口中的抽象方法

interface Info{

    void show();

}

enum Season1 implements Info{

    SPRING("春天","春暖花开"){

        @Override

        public void show() {

            System.out.println("春天在哪里？");

        }

    },

    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 Season1(String seasonName,String seasonDesc){

        this.seasonName = seasonName;

        this.seasonDesc = seasonDesc;

    }

    public String getSeasonName() {

        return seasonName;

    }

    public String getSeasonDesc() {

        return seasonDesc;

    }

    @Override

    public void show() {

        System.out.println("这是一个季节");

    }

}

可以对每一个枚举类的对象实现该接口，这样调用不同的对象，结果也就不一样。

巴特西

【Java】枚举类

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