Java泛型新的原始类型与泛型类型 [英] Java Generics new raw type vs generic type

问题描述

  ArrayList< String> 
我读了很多文章，但是无法理解这两行之间的区别。 list = new ArrayList（）; 
 ArrayList< String> list = new ArrayList< String>（）; 
  

唯一的区别是我看到第一行触发了Unchecked assignment警告。

解决方案

您可以创建一个原始列表。

  List list = new ArrayList（）; 
  

这很好，你现在有一个原始列表，你可以放入任何对象。如果你想把这个列表分配给一个打字版本，你将会做一个未经检查的任务。

  List< String> strings = list; 
  

这是因为，放入列表的内容从未被检查为字符串。

I read so many articles but I can't understand the difference between these two lines:

ArrayList<String> list = new ArrayList();
ArrayList<String> list = new ArrayList<String>();

The only difference I see that the first line trigger an "Unchecked assignment" warning.

解决方案

You could make a raw list.

List list = new ArrayList();

That is fine, you now have a raw list, that you can put any object into. If you want to assign that list to a typed version, you will make an unchecked assignment.

List<String> strings = list;

That is because, what was put into list was never checked to be a string.

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