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
