强制泛型方法的两个参数具有相同的具体类型 [英] Forcing two parameters of a generic method to have the same concrete type

问题描述

我怎样才能得到一个有两个参数的方法，这两个参数具有相同的具体类型？

How can I have a method with two parameters, with both parameters having the same concrete type?

例如，

For example,

boolean equals(Object a, Object b)

允许任何类型的 a 和任何类型的 b 。

allows for a of any type and b of any type.

我想强制 a 和 b 具有相同的具体类型。我试过

I want to force such that a and b have the same concrete type. I tried

<T> boolean equals(T a, T b)

并输入 Date 和一个 String 给该方法，期待编译时错误，但是我没有错误，因为T会解析为？扩展了Serializable& Comparable ，因为 Date 和 String implements Serializable 和 Comparable 。

and inputting a Date and a String to that method, expecting a compile-time error, but I get no errors, since T will resolve to ? extends Serializable & Comparable, since both Date and String implements Serializable and Comparable.

推荐答案

，基本上。没有办法做到这一点。即使你可以通过一个简单的调用来禁止不同类型的参数，也可以使用一个强制类型绕过：

You can't, basically. There's no way of doing that. Even if you could do it for a simple call to prohibit arguments of different types, it could always be bypassed using a cast:

equals((Object) date, (Object) string)

如果你对执行时间类型的参数，你只能在执行时测试它。编译器无法知道 Date 类型的参数是否具有正确引用的值 a java .util.Date 或一些子类。

If you're interested in the execution-time types of the arguments, you can only test that at execution time. There's no way of the compiler knowing whether an argument of type Date has a value which is a reference to precisely a java.util.Date or some subclass.

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