Java 枚举类

时间:2022-05-22 威斯布鲁克.猩猩人气:0

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

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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