枚举类

 A:枚举概述
    * 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。举例：一周只有7天，一年只有12个月等。
* B:回想单例设计模式：单例类是一个类只有一个实例
    * 那么多例类就是一个类有多个实例，但不是无限个数的实例，而是有限个数的实例。这才能是枚举类。

Demo1

public static void main(String[] args) {
　　Week mon = Week.MON;
　　Week tue = Week.TUE;
}

public class Week {

　　public static final Week MON = new Week();
　　public static final Week TUE = new Week();
　　public static final Week WED = new Week();

　　private Week(){}//私有构造，不让其它类创建本类对象
}

Demo2

public static void main(String[] args) {
　　Week2 mon = Week2.mon;
　　Week2 tue = Week2.mon;
　　Week2 wed = Week2.mon;
　　System.out.println(mon.getName());
　　tue.getName();
　　wed.getName();
}

有参构造

public class Week2 {
public static final Week2 mon = new Week2("星期一");
public static final Week2 tue = new Week2("星期二");
public static final Week2 wed = new Week2("星期三");

private String name;

private Week2(String name){
this.name = name;
}

public String getName() {
return name;
}
}

Demo3

public static void main(String[] args) {
　　Week3 mon = Week3.mon;
　　mon.show();
　　Week3 tue = Week3.tue;
　　tue.show();
　　Week3 wed = Week3.wed;
　　wed.show();
}

public static final Week3 mon = new Week3("星期一"){
public void show(){
System.out.println("星期一");
}
};
　　public static final Week3 tue = new Week3("星期二"){//父类引用指向子类对象
　　public void show(){
　　System.out.println("星期二");
　　};
};
public static final Week3 wed = new Week3("星期三"){
　　public void show(){
　　　　System.out.println("星期三");
　　}
　};
private String name;

private Week3(String name){
this.name = name;
}

public String getName() {
return name;
}
//编写一个抽象方法
public abstract void show();

 Demo4

public enum Week {
MON("星期一"),TUE("星期二"),WED("星期三");

private String name;
private Week(String name){
this.name=name;
}
public String getName() {
return name;
}

}

 

public static void main(String[] args) {
Week mon = Week.MON;
Week tue = Week.TUE;
Week wed = Week.WED;
System.out.println(mon.getName());
}