Java枚举（用Java普通类模拟枚举的实现原理及JDK枚举API使用示例）

枚举的特点：

◆类型安全（Type Safety） 
◆紧凑有效的枚举数值定义(Compact, Efficient Declaration of Enumerated Values) 
◆无缝的和程序其它部分的交互操作（Seamless integration with other language features） 
◆运行的高效率（Runtime efficiency）

详情请看：http://www.51cto.com/specbook/11/32877.htm

1、使用Java普通类模拟枚举的实现原理

import java.util.HashMap;
import java.util.Map;

/**
 * 模拟星期中的表示的天，每个星期天都表示一个对象
 * 1、类中的每一个枚举成员都是该类的一个实例对象
 * 2、构造函数私有化
 * 3、提供操作枚举成员的抽象方法和静态方法
 * @author 杨信
 *
 */
public abstract class WeekDate {
	
	/**
	 * 星期一
	 */
	public static final WeekDate MON = new WeekDate("MON",0) {	//匿名子类

		@Override
		public WeekDate nextDay() {
			return TUES;
		}

		@Override
		public WeekDate preDay() {
			return SUN;
		}
		
		@Override
		public String toString() {
			return "WeekDate.MON";
		}
		
	};	
	
	/**
	 * 星期二
	 */
	public static final WeekDate TUES = new WeekDate("TUES",1) {

		@Override
		public WeekDate nextDay() {
			return WEDNES;
		}

		@Override
		public WeekDate preDay() {
			return MON;
		}
		
		@Override
		public String toString() {
			return "WeekDate.TUES";
		}
	
	};
	
	/**
	 * 星期三
	 */
	public static final WeekDate WEDNES = new WeekDate("WEDNES",2) {

		@Override
		public WeekDate nextDay() {
			return THURS;
		}

		@Override
		public WeekDate preDay() {
			return TUES;
		}
		
		@Override
		public String toString() {
			return "WeekDate.WEDNES";
		}
		
	};
	
	/**
	 * 星期四
	 */
	public static final WeekDate THURS = new WeekDate("THURS",3) {

		@Override
		public WeekDate nextDay() {
			return FRI;
		}

		@Override
		public WeekDate preDay() {
			return WEDNES;
		}
		
		@Override
		public String toString() {
			return "WeekDate.THURS";
		}
		
	};
	
	/**
	 * 星期五
	 */
	public static final WeekDate FRI = new WeekDate("FRI",4){

		@Override
		public WeekDate nextDay() {
			return SATUR;
		}

		@Override
		public WeekDate preDay() {
			return THURS;
		}
		
		@Override
		public String toString() {
			return "WeekDate.FRI";
		}
		
	};
	
	/**
	 * 星期六
	 */
	public static final WeekDate SATUR = new WeekDate("SATUR",5){

		@Override
		public WeekDate nextDay() {
			return SUN;
		}

		@Override
		public WeekDate preDay() {
			return FRI;
		}
		
		@Override
		public String toString() {
			return "WeekDate.SATUR";
		}
		
	};
	
	/**
	 * 星期日
	 */
	public static final WeekDate SUN = new WeekDate("SUN",6){

		@Override
		public WeekDate nextDay() {
			return MON;
		}

		@Override
		public WeekDate preDay() {
			return SATUR;
		}
		
		@Override
		public String toString() {
			return "WeekDate.SUN";
		}

	};
	
	private static Map<String, WeekDate> valueMap = new HashMap<String, WeekDate>();
	
	/**
	 * 枚举名称
	 */
	private final String name;
	
	/**
	 * 枚举成员的顺序
	 */
	private final int ordinal;
	
	private WeekDate(String name,int ordinal) {
		this.name = name;
		this.ordinal = ordinal;
	}
	
	/**
	 * 保存枚举成员
	 */
	private static WeekDate[] values = {
		MON,TUES,WEDNES,THURS,FRI,SATUR,SUN
	};
	
	//初始化
	static {
		valueMap.put("MON", values[0]);
		valueMap.put("TUES", values[1]);
		valueMap.put("WEDNES", values[2]);
		valueMap.put("THURS", values[3]);
		valueMap.put("FRI", values[4]);
		valueMap.put("SATUR", values[5]);
		valueMap.put("SUN", values[6]);
	}
	
	/**
	 * 下一天
	 * @return
	 */
	public abstract WeekDate nextDay();
	
	/**
	 * 前一天
	 * @return
	 */
	public abstract WeekDate preDay();
	
	/**
	 * 枚举中的所有成员
	 * @return
	 */
	public static WeekDate[] values() {
		return values;
	}
	
	/**
	 * 将一个字符串转换成一个枚举成员对象
	 * @param name 枚举名称
	 * @return 枚举对象
	 */
	public static WeekDate valueOf(String name) {
		if (name.equalsIgnoreCase("MON")) {
			return MON;
		} else if (name.equalsIgnoreCase("TUES")) {
			return TUES;
		} else if (name.equalsIgnoreCase("WEDES")) {
			return WEDNES;
		} else if (name.equalsIgnoreCase("THURS")) {
			return THURS;
		} else if (name.equalsIgnoreCase("FRI")) {
			return FRI;
		} else if (name.equalsIgnoreCase("SATUR")) {
			return SATUR;
		} else if (name.equalsIgnoreCase("SUN")) {
			return SUN;
		} else {
			throw new IllegalArgumentException("找不到" + name + "枚举类型！");
		}
	}
	
	/**
	 * 优化字符串转枚举对象
	 * @param name 枚举名称
	 * @return 枚举对象
	 */
	public static WeekDate valueOf_2(String name) {
		WeekDate value = valueMap.get(name.toUpperCase());
		if (value == null) {
			throw new IllegalArgumentException("找不到" + name + "枚举类型！");
		}
		return value;
	}

	public String getName() {
		return name;
	}

	public int getOrdinal() {
		return ordinal;
	}
	
	/**
	 * 下一天
	 * @return
	 */
	/*public String nextDay() {
		if(this == MON) {
			return "TUES";
		} else if (this == TUES) {
			return "WEDNES";
		} else if (this == WEDNES) {
			return "THURS";
		} else if (this == THURS) {
			return "FRI";
		} else if (this == FRI) {
			return "SATUR";
		} else if (this == SATUR) {
			return "SUN";
		} else {
			return "MON";
		}
	}*/
	
	/**
	 * 前一天
	 */
	/*public String preDay() {
		if (this == MON) {
			//....
		} else if (...)....
	}*/
	
}

2、使用JDK5.0中提供的枚举特性改善普通类模拟枚举的功能

/**
 * 枚举的应用
 * 存储每周中的天份
 */
public enum WeekDateEnum {

	MON {
		
		@Override
		public WeekDateEnum nextDay() {
			return TUES;
		}
		
		@Override
		public WeekDateEnum preDay() {
			return SUN;
		}
		
	},  TUES {
		
		@Override
		public WeekDateEnum nextDay() {
			return WEDNES;
		}
		
		@Override
		public WeekDateEnum preDay() {
			return MON;
		}
		
	},  WEDNES {
		
		@Override
		public WeekDateEnum nextDay() {
			return THURS;
		}
		
		@Override
		public WeekDateEnum preDay() {
			return TUES;
		}
		
	},  THURS {
		
		@Override
		public WeekDateEnum nextDay() {
			return FRI;
		}
		
		@Override
		public WeekDateEnum preDay() {
			return WEDNES;
		}
		
	},  FRI {
		
		@Override
		public WeekDateEnum nextDay() {
			return SATUR;
		}
		
		@Override
		public WeekDateEnum preDay() {
			return THURS;
		}
		
	},  SATUR {
		
		@Override
		public WeekDateEnum nextDay() {
			return SATUR;
		}
		
		@Override
		public WeekDateEnum preDay() {
			return FRI;
		}
		
	},  SUN {
		
		@Override
		public WeekDateEnum nextDay() {
			return SATUR;
		}
		
		@Override
		public WeekDateEnum preDay() {
			return MON;
		}
		
	};

	private WeekDateEnum() {}
	
	/**
	 * 下一天
	 * @return
	 */
	public abstract WeekDateEnum nextDay();
	
	/**
	 * 前一天
	 * @return
	 */
	public abstract WeekDateEnum preDay();
	
	/**
	 * 枚举对象公共的toString方法，可以在case块中反馈自己想要返回的信息
	 */
	public String toString() {
		switch (this) {
		case MON:
			return "WeekDateEnum.MON";
		case TUES:
			return "WeekDateEnum.TUES";
		case WEDNES:
			return "WeekDateEnum.WEDNES";
		case THURS:
			return "WeekDateEnum.THURS";
		case FRI:
			return "WeekDateEnum.FRI";
		case SATUR:
			return "WeekDateEnum.SATUR";
		case SUN:
			return "WeekDateEnum.SUN";
		default:
			return null;
		}
	}
}

3、枚举功能测试

/**
 * 枚举功能测试
 */
public class EnumTest {

	public static void main(String[] args) {
		
		//使用普通JAVA类模拟枚举的应用
		WeekDate weekDate = WeekDate.MON;		//获得一个枚举对象
		//调用枚举中提供的方法
		System.out.println(weekDate.nextDay());	
		System.out.println(weekDate.preDay());
		System.out.println(weekDate.getName());
		//获得枚举成员所在枚举成员列表中的位置
		System.out.println(weekDate.getOrdinal());
		//调用某一个枚举成员的方法
		System.out.println(WeekDate.values()[0].preDay());
		System.out.println("---------------遍历枚举成员,普通JAVA类模拟--------------------------");
		for (WeekDate weekDate2 : WeekDate.values()) {
			System.out.println(weekDate2);
		}
		
		System.out.println("\n=================================================================\n");
		
		//使用JDK中提供的枚举特性功能应用
		WeekDateEnum weekDateEnum = WeekDateEnum.MON;	//获得一个枚举对象
		System.out.println(WeekDate.values().length); 	//获得枚举成员数量
		System.out.println(weekDateEnum.name());		//获得枚举的字符串名称
		System.out.println(weekDateEnum.toString());	//打印枚举对象，已重写toString方法，默认打印枚举的名称
		System.out.println(weekDateEnum.nextDay().ordinal());	//枚举成员列表中的位置
		System.out.println(WeekDateEnum.valueOf("FRI").nextDay().ordinal());
		System.out.println("---------------遍历枚举成员，使用JDK的枚举特性-------------------------");
		for (WeekDateEnum enumDemo : WeekDateEnum.values()) {
			System.out.println(enumDemo);
		}
		
	} 
	
}

4、测试结果