普通類實現枚舉與抽象類別的應用比較

當我們想實現一個星期幾的枚舉時候我們自己編寫一個類來實現！如果我們用實體類的代碼如下：

package com.jemsn.weekday;public class WeekDay {//建構函式私人化 讓別人不可以再建立新的對象執行個體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";}   }

然後我們在測試代碼裡調用它：

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

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

上面的代碼我們可以看出，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別，如下代碼：

package com.jemsn.weekday;public abstract class WeekDay {//建構函式私人化 讓別人不可以再建立新的對象執行個體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";}   }

上面的代碼中我們將if else分別轉化成了一個個獨立的類，測試代碼不變，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！