java中的枚举类

• 什么是枚举、枚举类？

枚举是指将变量的值一一列出来，变量的值只限于列举出来的值的范围内。例如：一周只有7天。

枚举类就是一个类有多个实例，但不是无限个数的实例。

• 创建无参构造对象的枚举类

（1）JDK1.5前：

public class Weekday {
    public static final Weekday MON = new Weekday();
    public static final Weekday TUE = new Weekday();
    public static final Weekday WED = new Weekday();
    public static final Weekday THU = new Weekday();
    public static final Weekday FRI = new Weekday();

    private Weekday(){}
}

创建对象：

public static void main(String[] args) {
        Weekday mon = Weekday.MON;
        Weekday tue = Weekday.TUE;
        Weekday wed = Weekday.WED;
        Weekday thu = Weekday.THU;
        Weekday fri = Weekday.FRI;
    }

（2）JDK1.5后：

public enum Weekday {
    MON,TUE,WED,THU,FRI;
}

创建对象和上面的方法一样。

• 创建有参构造对象的枚举类

（1）JDK1.5前：

public class Weekday {

    public static final Weekday MON = new Weekday("星期一");
    public static final Weekday TUE = new Weekday("星期二");
    public static final Weekday WED = new Weekday("星期三");
    public static final Weekday THU = new Weekday("星期四");
    public static final Weekday FRI = new Weekday("星期五");

    private String name;

    private Weekday(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

创建对象（和上面一样）：

public class Demo1 {
    public static void main(String[] args) {
        Weekday mon = Weekday.MON;
        Weekday tue = Weekday.TUE;
        Weekday wed = Weekday.WED;
        Weekday thu = Weekday.THU;
        Weekday fri = Weekday.FRI;
        System.out.println(mon.getName());   // 输出结果：星期一
    }
}

（2）JDK1.5后：

public enum Weekday2 {
    MON("星期一"),TUE("星期二"),WED("星期三"),THU("星期四"),FRI("星期五");

    private String name;

    private Weekday2(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

创建对象和上面的方法一样。

• 特殊情况：枚举类里面有抽象方法

（1）jdk1.5前：

public abstract class Weekday {

    public static final Weekday MON = new Weekday("星期一"){
        @Override
        public void show() {
            System.out.println("今天是星期一");               // 匿名类。父类引用指向子类对象。
        }
    };
    /*public static final Weekday TUE = new Weekday("星期二");
    public static final Weekday WED = new Weekday("星期三");
    public static final Weekday THU = new Weekday("星期四");
    public static final Weekday FRI = new Weekday("星期五");*/

    private String name;

    private Weekday(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public abstract void show();
}

（2）jdk1.5后：

public enum Weekday2 {
    MON("星期一"){
        @Override
        public void show() {
            System.out.println("今天是星期一");
        }
    },TUE("星期二") {
        @Override
        public void show() {
            System.out.println("今天是星期二");
        }
    },WED("星期三") {
        @Override
        public void show() {
            System.out.println("今天是星期三");
        }
    },THU("星期四") {
        @Override
        public void show() {
            System.out.println("今天是星期四");
        }
    },FRI("星期五") {
        @Override
        public void show() {
            System.out.println("今天是星期五");
        }
    };

    private String name;

    private Weekday2(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public abstract void show();
}