面向对象应用（一）

1.被客户不断变化的需求 “折磨”

第一次需求

class Printer{

    void Open(){

        System.out.println("Open");

    }

void Close(){

        System.out.println("Close");

    }
void Print(String s){

        System.out.println("Print--->" + s);

    }

}

1 class Test{

2     public static void main(String args []){

3         Printer printer = new Printer();

4         printer.Open();

5         printer.Print("abc");

6         printer.Close();

7     }

8 }

第二次需求

 1 class HPPrinter{

 2     void Open(){

 3         System.out.println("Open");

 4     }

 5

 6     void Close(){

 7         System.out.println("Close");

 8     }

 9

10     void Print(String s){

11         System.out.println("Print--->" + s);

12     }

13 }

 1 class CannonPrinter{

 2     void Open(){

 3         System.out.println("Open");

 4     }

 5

 6     void Close(){

 7         this.Clean();

 8         System.out.println("Close");

 9     }

10

11     void Print(String s){

12         System.out.println("Print--->" + s);

13     }

14

15     void Clean(){

16         System.out.println("Clean");

17     }

18 }

 1 class Test{

 2     public static void main(String args []){

 3         int flag = 0;

 4

 5         if( flag == 0){

 6             HPPrinter hpprinter = new HPPrinter();

 7             hpprinter.Open();

 8             hpprinter.Print("abc");

 9             hpprinter.Close();

10         }

11         else if( flag == 1){

12             CannonPrinter cannonprinter = new CannonPrinter();

13             cannonprinter.Open();

14             cannonprinter.Print("abc");

15             cannonprinter.Close();

16         }

17     }

18 }

第二次需求优化（消除重复代码）

 1 class Printer{

 2     void Open(){

 3         System.out.println("Open");

 4     }

 5

 6     void Close(){

 7         System.out.println("Close");

 8     }

 9

10     void Print(String s){

11         System.out.println("Print--->" + s);

12     }

13 }

1 class
HPPrinter extends Printer{2
}

 1 class CannonPrinter extends Printer{

 2     void Close(){

 3         this.Clean();

 4         super.Close();

 5     }

 6

 7     void Clean(){

 8         System.out.println("Clean");

 9     }

10 }

 1 class Test{

 2     public static void main(String args []){

 3         int flag = 1;

 4

 5         if( flag == 0){

 6             HPPrinter hpprinter = new HPPrinter();

 7             hpprinter.Open();

 8             hpprinter.Print("abc");

 9             hpprinter.Close();

10         }

11         else if( flag == 1){

12             CannonPrinter cannonprinter = new CannonPrinter();

13             cannonprinter.Open();

14             cannonprinter.Print("123");

15             cannonprinter.Close();

16         }

17     }

18 } 

面向对象应用（一）