通用方法的数组参数的Java类型推断

Question

Type inference doesn't seem to work for arrays with generic methods? I receive the error 'The method contains(T[], T) is not applicable for the arguments (int[], int)'. How should I be doing this?

method(new int[1], 0); //Error

...

public static <T> void method(T[] array, T value) {
    //Implement
}

Answer 1

您可以使用Integer而不是int，因为泛型不适用于基本类型。

Answer 2

Generics doesn't work with primitive types, only with object types.

You can do what looks like using generics with primitive types, due to auto-boxing:

<T> void methodOne(T value) {}

methodOne(1);  // Compiles OK, T = Integer.

What is actually happening here is that the int literal 1 is being "boxed" to Integer.valueOf(1) , which is an object of type Integer .

You can pass also an int[] to a generic method, because int[] is an object type itself. So:

methodOne(new int[1]);  // Compiles OK, T = int[].

However, you can't mix these two with the same type variable: int[] and Integer are not related types, so there is no single type variable T which is satisfied by both parameters. There is no equivalent auto-boxing operator from int[] to Integer[] .

As such, you would need to pass an Integer[] array as the first parameter:

method(new Integer[1], 0);

Answer 3

why use primitive type here. Generics only work with referenced type.

method(new int[1], 0); //Error

better to go with

 method(new Integer[]{1,2,3,4}, 0); //works fine