如何使用Java Enum

簡單的用法：JavaEnum簡單的用法一般用於代表一組常用常量，可用來代表一類相同類型的常量值。如：

性別：
public enum SexEnum {

  male, female;

}

顏色：
public enum Color {

  RED, BLUE,GREEN,BLACK;

}

 

枚舉對象里面的值都必須是唯一的。

可以通過Enum類型名直接引用該常量，如SexEnum.male,Color.RED.

復雜用法：Java為枚舉類型提供了一些內置的方法，同事枚舉常量還可以有自己的方法。可以很方便的遍歷枚舉對象，看個下面的例子：

1. 代碼一 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. 代碼二 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);

  }

}

輸出結果為：

Mon====>Monday

Tue====>Tuesday

Wed====>Wednesday

Thu====>Thursday

Fri====>Friday

Sat====>Saturday

Sun====>Sunday

Fri

 

 2.Java Enum原理
Java Enum類型的語法結構盡管和java類的語法不一樣，應該說差別比較大。但是經過編譯器編譯之后產生的是一個class文件。該class文件經過反編譯可以看到實際上是生成了一個類，該類繼承了java.lang.Enum.

WeekDay經過反編譯(javap WeekDay命令)之后得到的內容如下(去掉了匯編代碼)：

 

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);

}

 

所以實際上Enum類型就是以Java類來實現的，沒有什么新的特點，只不過java編譯器幫我們做了語法的解析和編譯。完全也可以自己實現。但是既然有這樣方便一個東西，當然會去用了。

使用實例：
1》：以Class定義的

public class PCUEnum {

 public static void main(String[] args) {
  System.out
    .println(PCUEnum.TaskStatus.get(PCUEnum.TaskStatus.DELETED));
 }


 public enum TaskStatus {
  // 1:等待執行 2:正在執行 3:執行完畢 4:執行失敗 5:暫停 100:已經刪除 101:已經送審
  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》：以類為實例：

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定義的

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定義

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定義

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());
    }
}