Java中enum的使用

在Java中，被 enum 关键字修饰的类型就是枚举类型，enum 的全称为 enumeration，它是 JDK 1.5 中引入的新特性。所有的枚举类型都是继承自Enum 类型。

以下是通过对枚举对象WeekDayEnum进行案例使用介绍：

public enum WeekDayEnum {

    //1、定义枚举常量，用逗号隔开，枚举类的后缀建议为Enum，
    // 枚举类的实例对象必须在最前面先定义
    // 枚举类型的实例对象建议全大写（这样做符合JAVA的规范）
    // 而且必须每个实例对象都必须维护上day、code私有成员变量
    MONDAY(1,"星期一"), //私有构造赋值
    TUESDAY(2,"星期二"), //私有构造赋值
    WEDNESDAY(3,"星期三"),//私有构造赋值
    THURSDAY(4,"星期四"), //私有构造赋值
    FRIDAY(5,"星期五"),//私有构造赋值
    SATURDAY(6,"星期六"), //私有构造赋值
    // 2.最后一行用分号结尾
    SUNDAY(7,"星期日");//私有构造赋值

    // 3、创建私有成员变量；
    private String day;
    private Integer code;

    //4、编写私有有参构造方法；
    // 枚举类型的构造函数默认为private，
    // 因为枚举类型的初始化要在当前枚举类中完成。
    private WeekDayEnum(Integer code,String day) {
        //System.out.println(weekday);
        this.code=code;
        this.day = day;
    }
    //5、覆盖toString()方法
    @Override
    public String toString() {
        return this.day+this.code;
    }

    //6.getWeekDayByCode
    public static WeekDayEnum getWeekDayByCode(Integer code){
        for (WeekDayEnum day : WeekDayEnum.values()){
            if (day.code.equals(code)){
                return day;
            }
        }
        return null;
    }

}

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public class WeekDayDemo {
    public static void main(String[] args) {
        //结果本质上都是WeekDayEnum对象，
        //底层相当于调用了WeekDayEnum默认构造方法创建一个对象，将所有的数据存入数组
        System.out.println(WeekDayEnum.MONDAY.getClass().getName());
        System.out.println(WeekDayEnum.MONDAY);
        System.out.println(WeekDayEnum.TUESDAY);
        System.out.println(WeekDayEnum.WEDNESDAY);
        System.out.println(WeekDayEnum.THURSDAY);
        System.out.println(WeekDayEnum.FRIDAY);
        System.out.println(WeekDayEnum.SATURDAY);
        System.out.println(WeekDayEnum.SUNDAY);

        //values方法用于将所有的枚举对象以数组的形式返回，方便使用
        System.out.println("values==="+WeekDayEnum.values());
        for (WeekDayEnum day : WeekDayEnum.values()){
            System.out.println(day.toString());
        }

        //通过valueOf，获取TUESDAY枚举类型
        WeekDayEnum day2 = WeekDayEnum.valueOf("TUESDAY");
        System.out.println("day2===="+day2);

        System.out.println(WeekDayEnum.getWeekDayByCode(2).toString());

        //使用枚举的结果本质上底层调用了WeekDayEnum默认构造方法，
        //创建了多个WeekDayEnum实例对象，对象起名分别为MONDAY到SUNDAY，
        //将枚举数据实例存入一个数组的里面，ordinal是数组的下标
        System.out.println(WeekDayEnum.MONDAY.ordinal());
        System.out.println(WeekDayEnum.TUESDAY.ordinal());
        System.out.println(WeekDayEnum.WEDNESDAY.ordinal());
        System.out.println(WeekDayEnum.THURSDAY.ordinal());
        System.out.println(WeekDayEnum.FRIDAY.ordinal());
        System.out.println(WeekDayEnum.SATURDAY.ordinal());
        System.out.println(WeekDayEnum.SUNDAY.ordinal());
    }
}

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