深入浅出讲解Java中的枚举类

背景: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)

> 季节:Spring(春节).……..Winter(冬天)

> 支付方式:Cash(现金)、WeChatPay(微信)、Alipay(支付宝)BankCard(银

行卡)、CreditCard(信用卡)

> 就职状态:Busy、Free、Vocation、Dimission

> 订单状态:Nonpayment(未付款)、Paid(已付款)、Fulfilled(已配货)、

Delivered(已发货)、Return退货》Checked已确认)

> 线程状态:创建、就绪、运行、阻塞、死立

一、枚举类的使用

1.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

2.当需要定义一组常量时,强烈建议使用枚举类

3.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。

二、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 spring = Season.SPRING;
        System.out.println(spring);
    }
}
    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.提供当前枚举类的对各对象: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2:提供toString()
        @Override
        public String toString() {
            return "Season{" +
                    "seasonName='" + seasonName + '\'' +
                    ", seasonDesc='" + seasonDesc + '\'' +
                    '}';
        }
    }

方式二:JDK5.0之后,可以使用enum关键字定义枚举类

FEC15C46-F430-10AC-9515-AE7969628373.png

public class SeasonTest1 {
    public static void main(String[] args) {
        Season1 summer = Season1.SUMMER;
        System.out.println(summer);
        System.out.println(Season1.class.getSuperclass());//java.lang.Enum
        //values():
        Season1[] values = Season1.values();
        for (int i = 0; i < values.length; i++) {
            System.out.println(values[i]);
        }
        //valueOf(String objName):返回枚举类中对象时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);
//        winter.show();
    }
    //使用enum关键字定义枚举类
    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");
        //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 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;
        }

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