Java枚举

Java枚举是一个类，枚举里面的元素相当于该类的实例对象。

 

声明一个枚举对象，元素列表位于最前面

 

enum WeekDay {
	SUN, MON, TUE, WED, THU, FRI, SAT;
}

 

获取一个枚举元素

 

WeekDay weekDay = WeekDay.SUN;
System.out.println(weekDay); //SUN
System.out.println(weekDay.name()); //SUN
System.out.println(weekDay.ordinal()); //返回该元素的位置 0

 

枚举类有两个个非常重要的静态方法

 

1、将字符串变为枚举对象，前提是字符串值和枚举元素名是一样的。

valueOf(String arg0)

 

System.out.println(WeekDay.valueOf("SAT")); //SAT

 

2、获得枚举元素的数组对象

values()

 

WeekDay.values().length //7

 

带有构造方法，属性，方法的枚举对象，其中构造方法一定是私有的

 

enum WeekDay {
	SUN(0), MON(1), TUE(2), WED(3), THU(4), FRI(5), SAT(6);
	private int day;

	private WeekDay(int day) {
		this.day = day;
	}

	public static WeekDay nextDay(int day) {
		WeekDay weekDay = null;
		switch (day) {
		case 0:
			weekDay = WeekDay.MON;
			break;
		case 1:
			weekDay = WeekDay.TUE;
			break;
		case 2:
			weekDay = WeekDay.WED;
			break;
		case 3:
			weekDay = WeekDay.THU;
			break;
		case 4:
			weekDay = WeekDay.FRI;
			break;
		case 5:
			weekDay = WeekDay.SAT;
			break;
		case 6:
			weekDay = WeekDay.SUN;
			break;
		default:
			weekDay = WeekDay.SUN;
		}
		return weekDay;
	}

	public static WeekDay nextDay(WeekDay weekDay) {
		return nextDay(weekDay.getDay());
	}

	public WeekDay nextDay() {
		return nextDay(this.getDay());
	}

	public int getDay() {
		return day;
	}

	public void setDay(int day) {
		this.day = day;
	}
}

 

以下部分参考自：http://softbeta.iteye.com/blog/1185573

 

switch支持枚举类

 

enum Signal {
	GREEN, YELLOW, RED
}
public class TrafficLight {
	Signal color = Signal.RED;
	public void change() {
		switch (color) {
		case RED:
			color = Signal.GREEN;
			break;
		case YELLOW:
			color = Signal.RED;
			break;
		case GREEN:
			color = Signal.YELLOW;
			break;
		}
	}
}

 

由于枚举类统一继承自java.lang.Enum类，所以自定义枚举类只能实现接口，不能在继承其他类了。

 

public interface Behaviour {
	void print();
	String getInfo();
}
public enum Color implements Behaviour{
	RED("红色", 1), GREEN("绿色", 2), BLANK("白色", 3), YELLO("黄色", 4);
	// 成员变量
	private String name;
	private int index;
	// 构造方法
	private Color(String name, int index) {
		this.name = name;
		this.index = index;
	}
//接口方法
	@Override
	public String getInfo() {
		return this.name;
	}
	//接口方法
	@Override
	public void print() {
		System.out.println(this.index+":"+this.name);
	}
}

 

实现带有抽象方法的枚举

 

enum TrafficLight {
	RED {
		@Override
		public TrafficLight next() {
			return GREEN;
		}

	},
	GREEN {
		@Override
		public TrafficLight next() {
			return YELLOW;
		}
	},
	YELLOW {
		@Override
		public TrafficLight next() {
			return RED;
		}
	};
	public abstract TrafficLight next();
}