如何使用Java Enum

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

1. 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());
    }
}