括号内和括号外的Java通用方法参数类型 [英] Java generic method parameter type inside brackets vs. outside brackets

问题描述

两者之间是否有任何区别

Is there any difference between:

static void findMax(LinkedList<? extends Number> list){...}

和:

static <T extends Number> void findMax(LinkedList<T> list){...}

由于两者都有效，所以我想知道两者之间是否有较大的区别，建议使用.

Since both work, I'd like to know if there's any big difference between the two and which is advised.

推荐答案

主要区别在于，在第二个版本中，您可以访问类型T，而在第一个版本中，您不能访问类型.

The main difference is that in the second version you can access the type T whereas in the first one you can't.

例如，您可能想返回链接到T的内容(例如，返回T而不是void):

For example, you might want to return something linked to T (e.g. returning T instead of void):

static <T extends Number> T findMax(LinkedList<T> list){...}

或者您可能需要创建一个新的Ts列表:

Or you might need to create a new list of Ts:

static <T extends Number> void findMax(LinkedList<T> list){
    List<T> copyAsArrayList = new ArrayList<> (list);
    //do something with the copy
}

如果您不需要访问T，则两个版本在功能上都是等效的.

If you don't need access to T, both versions are functionally equivalent.

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