單一職責原則

——專心致誌只做一件事

 1 package danyizhize;
 2 
 3 class SunWuKong {
 4     public void XiangMo(String name) {
 5         System.out.println(name + "降魔！");
 6     }
 7 
 8     public void XingLi(String name) {
 9         System.out.println(name + "拿行李！");
10     }
11 
12     public void QianMa(String name) {
 
13         System.out.println(name + "牽白龍馬!");
14     }
15 
16     public void QiMa(String name) {
17         System.out.println(name + "騎馬!");
18     }
19 }
20 
21 public class DanYiZhiZe {
22 
23     public static void main(String[] args) {
24         // TODO Auto-generated method stub
25         SunWuKong sunWuKong = new
 
 SunWuKong();
26         sunWuKong.XiangMo("孫悟空");
27         sunWuKong.QianMa("孫悟空");
28         sunWuKong.XingLi("孫悟空");
29         sunWuKong.QiMa("孫悟空");
30     }    
31 }

運行結果：

孫悟空降魔！
孫悟空牽白龍馬!
孫悟空拿行李！
孫悟空騎馬!

孫悟空的任務太多，忙不過來！！！

 1 package danyizhize;
 2 
 3 class SunWuKong {
 4     public
 
 void XiangMo(String name) {
 5         System.out.println(name + "降魔！");
 6     }
 7 }
 8 
 9 class ZhuBaJie {
10     public void QianMa(String name) {
11         System.out.println(name + "牽白龍馬!");
12     }
13 }
14 
15 class ShaHeShang {
16     public void XingLi(String name) {
17         System.out.println(name + "拿行李！");
18     }
19 }
20 
21 class TangSeng {
22     public void QiMa(String name) {
23         System.out.println(name + "騎馬!");
24     }
25 }
26 
27 public class DanYiZhiZe {
28 
29     public static void main(String[] args) {
30         // TODO Auto-generated method stub
31         SunWuKong sunWuKong = new SunWuKong();
32         ZhuBaJie zhuBaJie = new ZhuBaJie();
33         ShaHeShang shaHeShang = new ShaHeShang();
34         TangSeng tangSeng = new TangSeng();
35 
36         sunWuKong.XiangMo("孫悟空");
37         zhuBaJie.QianMa("豬八戒");
38         shaHeShang.XingLi("沙和尚");
39         tangSeng.QiMa("唐僧");
40     }
41 }

運行結果：

孫悟空降魔！
豬八戒牽白龍馬!
沙和尚拿行李！
唐僧騎馬!

改動大，將原有的1個類變成了4個類，還需要修改客戶端代碼！！！

 1 package danyizhize;
 2 
 3 class Person {
 4     public void Work(String name) {
 5         if ("孫悟空".equals(name)) {
 6             System.out.println(name + "降魔！");
 7         } else if ("豬八戒".equals(name)) {
 8             System.out.println(name + "牽白龍馬！");
 9         } else if ("沙和尚".equals(name)) {
10             System.out.println(name + "拿行李！");
11         } else if ("唐僧".equals(name)) {
12             System.out.println(name + "騎馬！");
13         }
14     }
15 }
16 
17 public class DanYiZhiZe {
18 
19     public static void main(String[] args) {
20         // TODO Auto-generated method stub
21         Person person = new Person();
22 
23         person.Work("孫悟空");
24         person.Work("豬八戒");
25         person.Work("沙和尚");
26         person.Work("唐僧");
27     }
28 }

運行結果：

孫悟空降魔！
豬八戒牽白龍馬！
沙和尚拿行李！
唐僧騎馬！

如果再增加其他人，很有可能變成孫悟空做飯，操作簡單，卻存在隱患！！！

 1 package danyizhize;
 2 
 3 class Person {
 4     public void XiangMo(String name) {
 5         System.out.println(name + "降魔！");
 6     }
 7 
 8     public void XingLi(String name) {
 9         System.out.println(name + "拿行李！");
10     }
11 
12     public void QianMa(String name) {
13         System.out.println(name + "牽白龍馬!");
14     }
15 
16     public void QiMa(String name) {
17         System.out.println(name + "騎馬!");
18     }
19 }
20 
21 public class DanYiZhiZe {
22 
23     public static void main(String[] args) {
24         // TODO Auto-generated method stub
25         Person person = new Person();
26         person.XiangMo("孫悟空");
27         person.QianMa("豬八戒");
28         person.XingLi("沙和尚");
29         person.QiMa("唐僧");
30     }
31 }

孫悟空降魔！
豬八戒牽白龍馬!
沙和尚拿行李！
唐僧騎馬!

需要足夠簡單的邏輯，才可以在代碼上違反單一職責原則；

需要類中方法數量足夠少，才可以在方法級別上違反單一職責原則。

西遊記之設計模式原則——單一職責原則