接口的应用

1 interface Printer{
2     void Open();    
3     void Close();    
4     void Print(String s);
5 }

 1 class HPPrinter implements Printer{
 2     public void Open(){         //少写public报错 
 3                                              //自己的理解父类是public, 
 4                                              //复写时必须权限大于public
 5         System.out.println("HP Open");
 6     }    
 7     public void Close(){
 8         System.out.println("HP Close");
 9     }    
10     public void Print(String s){
11         System.out.println("HP Print--->" + s );
12     }
13 }

 1 class CannonPrinter implements Printer{
 2     private void Clean(){
 3         System.out.println("Cannon Clean");
 4     }
 5     
 6     public void Close(){
 7         this.Clean();
 8         System.out.println("Cannon Close");
 9     }
10     
11     public void Open(){
12         System.out.println("Cannon Open");
13     }
14     
15     public void Print(String s){
16         System.out.println("Cannon Print--->" + s );
17     }
18 }

 1 class Test{
 2     public static void main(String args []){
 3         Printer printer = null ;        
 4         int flag = 0;        
 5         if( flag == 0){
 6             printer = new HPPrinter();
 7         }
 8         else if( flag == 1){
 9             printer = new CannonPrinter();
10         }
11         printer.Open();
12         printer.Print("123");
13         printer.Close();
14     }
15 }

 1 class Test{
 2     public static void main(String args []){
 3         int flag = 1 ;
 4         Printer printer = PrinterFactory.getPrinter(flag); 
 5                     
 6         printer.Open();
 7         printer.Print("123");
 8         printer.Close();
 9     }
10 }

 1 class PriterFactory(){
 2     public static Printer getPrinter(int flag){   //static便于调用
 3                                                   //返回值类型是Printer
 4                                                   //函数名是getPrinter
 5         Printer printer = null ;                
 6         if( flag == 0){
 7             printer = new HPPrinter();
 8         }
 9         else if( flag == 1){
10             printer = new CannonPrinter();
11         }
12         return printer;
13     } 
14 }