Java泛型中的一些困惑 [英] A little confusion in java Generics

问题描述

List<String> l=new ArrayList<String>()

和

List<String> l=new ArrayList();

可以帮助任何人，原则是什么?

谢谢！

Can help anyone help and what is the principle?

Thanks!

推荐答案

只要左侧的Generic设置了类型，就差不多了.

但是，如果不设置左侧值的类型，可能会导致奇怪的情况:value:

That''s pretty much the same as long as the Generic on the left side is set with a type.

But it can lead to strange situations when you do not set the type of the left sided value: value:

List l = new ArrayList<string>();
List<Object> o = l;

在将内容添加到列表中时，这肯定可行，因为String是一个对象.

That certainly works while adding things to the List, because String is an Object.

o.add(new Object());
o.add("String");

但是，当您获取值时，可能会导致行为异常:

But when you''re fetching the values, it can lead to misbehavior:

System.out.println(o.get(0)); // Exception because value(0) is no String.

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