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

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());
    }
}