當我們想實現一個星期幾的列舉時候我們自己編寫一個類來實現！如果我們用實體類的程式碼如下：

package com.jemsn.weekday;

public class WeekDay {
	//建構函式私有化 讓別人不可以再建立新的物件例項
	private WeekDay () {}
   public static final WeekDay MonDay=new WeekDay();
   public static final WeekDay Tuesay=new WeekDay();
   public static final WeekDay WendsDay=new WeekDay();
   public static final WeekDay ThusDay=new WeekDay();
   public static final WeekDay FriDay=new WeekDay();
   public static final WeekDay StaDay=new WeekDay();
   public static final WeekDay SunDay=new WeekDay();
   //如果我們要一個NextDay()方法
   public WeekDay NextDay() {
	   if(this==MonDay){
		   return Tuesay;
	   }else if(this==Tuesay){
		   return WendsDay;
	   }	   
	   else if(this==WendsDay){
		   return ThusDay;
	   }
	   else if(this==ThusDay){
		   return FriDay;
	   }
	   else if(this==FriDay){
		   return StaDay;
	   }
	   else if(this==StaDay){
		   return SunDay;
	   }else {
		return MonDay;
	}
	
	 
}
 //重寫ToString方法
public String toString() {
	 return this==MonDay?"星期一":this==Tuesay?"星期二":this==WendsDay?"星期三":this==ThusDay?"星期四":"星期五";
}
   
}
 

然後我們在測試程式碼裡呼叫它：

package com.jemsn.weekday;

public class test {
  
	public static void main(String[] args) {
		WeekDay monday=WeekDay.MonDay;
		WeekDay tuesday=WeekDay.Tuesay;
		System.out.println(monday.NextDay());
		System.out.println(tuesday.NextDay());
	}

}

輸出結果如下：

-----------------------------------------------------------------------

星期二
星期三

-----------------------------------------------------------------------

上面的程式碼我們可以看出，在我們的NextDay方法中用了一大堆的if else else if 之類的，如果我們裝基改為抽象類，如下程式碼：

package com.jemsn.weekday;

public abstract class WeekDay {
	//建構函式私有化 讓別人不可以再建立新的物件例項
	private WeekDay () {}
   public static final WeekDay MonDay=new WeekDay(){
 
	public WeekDay NextDay() {
		return WeekDay.Tuesay;
	}
	   
   };
   //採用了匿名內部類的實現方式
   public static final WeekDay Tuesay=new WeekDay(){
	   
		public WeekDay NextDay() {
			return WeekDay.WendsDay;
		}
		   
	   };
   public static final WeekDay WendsDay=new WeekDay(){
	   
		public WeekDay NextDay() {
			return WeekDay.ThusDay;
		}
		   
	   };
   public static final WeekDay ThusDay=new WeekDay(){
	   
		public WeekDay NextDay() {
			return WeekDay.FriDay;
		}
		   
	   };
   public static final WeekDay FriDay=new WeekDay(){
	   
		public WeekDay NextDay() {
			return WeekDay.StaDay;
		}
		   
	   };
   public static final WeekDay StaDay=new WeekDay(){
	   
		public WeekDay NextDay() {
			return WeekDay.SunDay;
		}
		   
	   };
   public static final WeekDay SunDay=new WeekDay(){
	   
		public WeekDay NextDay() {
			return WeekDay.MonDay;
		}
		   
	   };
   //如果我們要一個NextDay()方法
   public abstract WeekDay NextDay(); 
	
	 

 //重寫ToString方法
public String toString() {
	 return this==MonDay?"星期一":this==Tuesay?"星期二":this==WendsDay?"星期三":this==ThusDay?"星期四":"星期五";
}
   
}
 

上面的程式碼中我們將if else分別轉化成了一個個獨立的類，測試程式碼不變，輸出的結果如下 ：

-----------------------------------------------------------------------

星期二
星期三

-----------------------------------------------------------------------

我們看到的還是一樣，但是實現的方式卻完全不一樣！所以我們可以總結用抽象方法結合匿名內部類實現比統一的更加好！