java 泛型学习

 1 import java.util.ArrayList;
 2 import java.util.Collection;
 3 
 4 class  A< T extends Collection>
 5 {
 6     private T x;
 7     public A(T x)
 8     {
 9         this.x=x;
10 
11     }
12     public T get()
13     {
14         return this.x;
15     }
16     
17     
18 }
19 public class CollectionGenFoo
20 {
21     public static void main(String args[])
22     {
23         A<ArrayList> a=new A<ArrayList>(new ArrayList());
24         System.out.println(a.get());
25         //A<Collection> a1=new A<ArrayList>(new ArrayList());
26         A< ? extends Collection> a1=new A<ArrayList>(new ArrayList());
27         
28         
29         
30         
31         
32         
33     }
34     
35     }