泛型-函数返回类型是否与参数类型相同? [英] Generics - Function return type the same as the parameter type?

问题描述

我想创建一个函数，该函数返回与所传入参数的数据类型相同的数据类型的 List .例如，我将这样调用该函数:

I want to make a function which returns a List of a data type the same as the data type of the parameter that was passed in. For example, I would call the function like this:

Object a = new Object();
List<Object> aList = foo(a);

Integer b = 5;
List<Integer> bList = foo(b);

因为我将 Object 传递给 foo ，所以它向我返回了 List< Object> .当我传递 Integer 时，会提供 List< Integer> .

Because I passed an Object to foo, it returned a List<Object> to me. When I pass an Integer, a List<Integer> is provided.

如果这不可能，我也可以使用如下语法:

If this is not possible, I'm also okay with syntax like:

Object a = new Object();
List<Object> aList = foo(Object.class, a);

之前我已经使用过泛型很多次了，但是我不知道如何在返回类型中定义数据类型，然后说该参数将使用相同的数据类型.

I've used generics plenty of times before but I don't know how to define a data type in the return type, and then say that the same data type will be used for the parameter.

List<T> foo(T data)
{
   ...
}

还是必须像....列表< T扩展对象> ?我以前从未做过这种高级的泛型.

Or would it have to be like.... List<T extends Object>? I've never done generics this advanced before.

推荐答案

您需要在函数的返回类型之前指定泛型类型:

You need to specify the generic type right before the return type of the function say:

public static <T> List<T> foo(T data) {
    return new ArrayList<>();
}

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