Java – use generic wildcards instead of interfaces

If you want to store an array of objects of type myinterface, is it acceptable to use the second form of the first form?

i) Use only one interface: –

List<MyInterface> mylist = new ArrayList<MyInterface>();@H_403_5@ 
 
ii)使用通用通配符：
 
  
 
List<? extends MyInterface> mylist = new ArrayList<? extends MyInterface>();@H_403_5@ 
 
编辑：
 
 
正如迄今为止的答案所指出的,第二号不会编译.我和案例之间有什么区别iii其中：
 
 
iii)仅在引用中使用通配符： – 
 
  
 
List<? extends MyInterface> mylist = new ArrayList<MyInterface>();@H_403_5@

Solution
The second will not compile Imagine:
A implements MyInterface
B implements MyInterface@H_403_5@ 
 
那么以下将匹配您的第二个表达式,但不会编译：
 
  
 
// incorrect
List<A> mylist = new ArrayList<B>();@H_403_5@ 
 
更正错误：
 
  
 
List<? extends MyInterface> mylist = new ArrayList<MyInterface>();@H_403_5@ 
 
在某种意义上说它是编译的,但是你不能添加MyInterface的任何子类.令人困惑,但正确 – 在我阅读说明之后.同样的原因：通配符可以被看作例如：
 
  
 
// I kNow this is not compileable; this is internal compiler "thinking".
// Read it as "somewhere someone may instantiate an ArrayList<A> and pass 
// it down to us; but we cannot accept it as something that Could be 
// potentially used as List<B>"
List<A> mylist = new ArrayList<MyInterface>();@H_403_5@ 
 
所以这不行：
 
  
 
mylist.add(b);@H_403_5@ 
 
反之亦然.编译器拒绝做这些可能不正确的操作.
 
 
允许您将MyInterface的任何子类添加到mylist的选项是：
 
  
 
List<MyInterface> mylist = new ArrayList<MyInterface>();@H_403_5@