java design pattern - strategy pattern

Strategy pattern also known as Policy Pattern. 

挺有意思的看了一个例子，将不通的Algorithm 设计为不同的类，然后通过一个Context 类联系在一起。

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1. package policypattern;
   
2. 
   
3. interface Strategy{
   
4.     public void sort(int[] numbers);
   
5. }
   
6. 
   
7. class MyContext{
   
8.     private Strategy strategy;
   
9. 
   
10.     //constructor
    
11.     public MyContext(Strategy strategy){
    
12.         this.strategy= strategy;
    
13.     }
    
14. 
    
15.     public void arrange(int[] input){
    
16.         strategy.sort(input);
    
17.     }
    
18. }
    
19. 
    
20. class BubbleSort implements Strategy{
    
21.     @Override
    
22.     public void sort(int[] numbers){
    
23.         System.out.println("Sorting array using bubble sort strategy");
    
24.     }
    
25. }
    
26. 
    
27. class InsertionSort implements Strategy{
    
28. 
    
29.     @Override
    
30.     public void sort(int[] numbers){
    
31.         System.out.println("Sorting array with insertion sort strategy");
    
32.     }
    
33. }
    
34. 
    
35. 
    
36. class MergeSort implements Strategy{
    
37.     @Override
    
38.     public void sort(int[] numbers){
    
39.         System.out.println("Sorting array using merge sort strategy");
    
40.     }
    
41. }
    
42. 
    
43. class QuickSort implements Strategy{
    
44.     @Override
    
45.     public void sort(int[] numbers){
    
46.         System.out.println("Sorting array using quick sort strategy");
    
47.     }
    
48. }
    
49. 
    
50. 
    
51. 
    
52. public class StrategyPatternDemo {
    
53.     public static void main(String[] args){
    
54.         int[] var = {1,2,9,6,4,10};
    
55. 
    
56.         //provide any strategy to do the sorting
    
57.         MyContext ctx = new MyContext(new BubbleSort());
    
58.         ctx.arrange(var);
    
59. 
    
60.         //we can change the Strategy without changing Context class
    
61.         ctx = new MyContext(new QuickSort());
    
62.         ctx.arrange(var);
    
63.     }
    
64. }