简单的用法:JavaEnum简单的用法一般用于代表一组常用常量,可用来代表一类相同类型的常量值。如:
性别:
public enum SexEnum { male, female; } 颜色:
public enum Color { RED, BLUE,GREEN,BLACK; }
枚举对象里面的值都必须是唯一的。
可以通过Enum类型名直接引用该常量,如SexEnum.male,Color.RED.
复杂用法:Java为枚举类型提供了一些内置的方法,同事枚举常量还可以有自己的方法。可以很方便的遍历枚举对象,看个下面的例子:
1. 代码一 WeekDay.java: public enum WeekDay { Mon("Monday"), Tue("Tuesday"), Wed("Wednesday"), Thu("Thursday"), Fri( "Friday"), Sat("Saturday"), Sun("Sunday"); private final String day; private WeekDay(String day) { this.day = day; } public static void printDay(int i){ switch(i){ case 1: System.out.println(WeekDay.Mon); break; case 2: System.out.println(WeekDay.Tue);break; case 3: System.out.println(WeekDay.Wed);break; case 4: System.out.println(WeekDay.Thu);break; case 5: System.out.println(WeekDay.Fri);break; case 6: System.out.println(WeekDay.Sat);break; case 7: System.out.println(WeekDay.Sun);break; default:System.out.println("wrong number!"); } } public String getDay() { return day;
}
}
1. 代码二 WeekDayTest.java:
public class WeekDayTest { public static void main(String args[]) { for (WeekDay day : WeekDay.values()) { System.out.println(day + "====>" + day.getDay());
}
WeekDay.printDay(5); } } 输出结果为: Mon====>Monday Tue====>Tuesday Wed====>Wednesday Thu====>Thursday Fri====>Friday Sat====>Saturday Sun====>Sunday Fri
2.Java Enum原理
Java Enum类型的语法结构尽管和java类的语法不一样,应该说差别比较大。但是经过编译器编译之后产生的是一个class文件。该class文件经过反编译可以看到实际上是生成了一个类,该类继承了java.lang.Enum.
WeekDay经过反编译(javap WeekDay命令)之后得到的内容如下(去掉了汇编代码):
public final class WeekDay extends java.lang.Enum{ public static final WeekDay Mon; public static final WeekDay Tue; public static final WeekDay Wed; public static final WeekDay Thu; public static final WeekDay Fri; public static final WeekDay Sat; public static final WeekDay Sun; static {}; public static void printDay(int); public java.lang.String getDay(); public static WeekDay[] values(); public static WeekDay valueOf(java.lang.String); }
所以实际上Enum类型就是以Java类来实现的,没有什么新的特点,只不过java编译器帮我们做了语法的解析和编译。完全也可以自己实现。但是既然有这样方便一个东西,当然会去用了。
使用实例:
1》:以Class定义的
public class PCUEnum { public static void main(String[] args) {
System.out
.println(PCUEnum.TaskStatus.get(PCUEnum.TaskStatus.DELETED));
} public enum TaskStatus {
// 1:等待执行 2:正在执行 3:执行完毕 4:执行失败 5:暂停 100:已经删除 101:已经送审
NOTINQUEUE,WAITING, EXECUTING, EXECUTED, FAILED, SUSPEND, DELETED,WAITING_AUDIT; public static int get(TaskStatus s) {
int result = 0;
switch (s) {
case NOTINQUEUE:
result=0;
break;
case WAITING:
result = 1;
break;
case EXECUTING:
result = 2;
break;
case EXECUTED:
result = 3;
break;
case FAILED:
result = 4;
break;
case SUSPEND:
result = 5;
break;
case DELETED:
result = 100;
break;
case WAITING_AUDIT:
result = 101;
break;
}
return result;
}
} }
1.1》:以类为实例:
public class EnumClass { enum explore {
HERE, THERE
} enum WeekDay {
Mon("Monday"), Tue("Tuesday"), Wed("Wednesday"), Thu("Thursday"), Fri("Friday"), Sat("Saturday"),
Sun("Sunday"), Wro("Wrong day"); private String day; WeekDay(String day){
this.day = day;
} public String getDay() {
return day;
}
} public static void main(String[] args) {
System.out.println(EnumClass.explore.HERE); System.out.println("--------"); for(EnumClass.WeekDay day : EnumClass.WeekDay.values()) {
System.out.println(day.getDay());
}
}
}
2》:以Enum定义的
package com.zhou.test; public enum TaskEnumStatus { NOTINQUEUE(1),WAITING(2), EXECUTING(3), EXECUTED(4), FAILED(5), SUSPEND(6), DELETED(7),WAITING_AUDIT(8); private int i; private TaskEnumStatus(int i) { this.i = i; } public int getEnumStatus() { return i; } }
public static void main(String[] args) { System.out.println(TaskEnumStatus.NOTINQUEUE + "=" + TaskEnumStatus.NOTINQUEUE.getEnumStatus()); }
2.1》:以Enum定义
public enum UserStatusEnum {
DISABLE("disable"),
ENABLE("enable"); private String value; UserStatusEnum(String value){
this.value = value;
} public String getValue() {
return value;
} public String toString() {
return value;
} public static void main(String[] args) {
System.out.println(UserStatusEnum.DISABLE);
}
}
2.2》:以Enum定义
public enum NumberEnum {
CONST_FOUR(4), CONST_ENIGHT(8), CONST_NINE(999999);
private final int value; NumberEnum(int value) {
this.value = value;
} public int getValue() {
return value;
} public static void main(String[] args) {
System.out.println(NumberEnum.CONST_ENIGHT.getValue());
}
}