使用普通类实现枚举类型

使用普通类黄实现绿红3个颜色的枚举

class ColarEnum {
	//私有化防止外部实例化此类
	private ColarEnum(){}
	//转化为字符串以便输出
	public String toString(){
		if(this == GREEN)
			return "GREEN";
		elseif(this == YELLOW)
			return "YELLOW";
		else
			return "RED";
	}
	//构造函数私有化后,只能在内部设定枚举值,此处为GREEN,YELLOW,RED
	public static final ColarEnum GREEN = new ColarEnum();
	//static,final顺序无关紧要
	public final static ColarEnum YELLOW = new ColarEnum();
	public final static ColarEnum RED = new ColarEnum();
}
public class EnumTest {
	public static void main(String[] args) {
		ColarEnum A = ColarEnum.GREEN;
		ColarEnum B = ColarEnum.YELLOW;
		ColarEnum C = ColarEnum.RED;
		System.out.println(A.toString());
		System.out.println(B.toString());
		System.out.println(C.toString());
	}
}

关联3个颜色,GREEN→YELLOW→RED→GREEN..

//使用抽象方法,类也变为抽象
abstract class ColarEnum {
	private ColarEnum(){}
	//抽象方法
	public abstract ColarEnum next();
	public String toString(){
		if(this == GREEN)
			return "GREEN";
		if(this == YELLOW)
			return "YELLOW";
		else
			return "RED";
	}
	//每个元素来实现自己的next方法
	public static final ColarEnum GREEN = new ColarEnum(){
		public ColarEnum next(){
			return YELLOW;
		}
	};
	public final static ColarEnum YELLOW = new ColarEnum(){
		public ColarEnum next(){
			return RED;
		}
	};
	public final static ColarEnum RED = new ColarEnum(){
		public ColarEnum next(){
			return GREEN;
		}
	};
}
public class EnumTestCP {

	public static void main(String[] args) {
		ColarEnum A = ColarEnum.GREEN;
		System.out.println(A.toString());
		System.out.println(A.next().toString());
		System.out.println(A.next().next().toString());
	}
}