从Object extends Number获取原始值？ [英] Get primitive value from Object extends Number?

问题描述

我正在尝试创建一个类，可以处理减去，添加，更新给定类型的数字（扩展数字的任何东西）。

I am trying to make a class that can process subtracting, adding, updating for number with given type (anything that extends Number).

public class DynamicNumber<T extends Number> {

    private T number;

    public DynamicNumber(T number) {
        this.number = number;
    }

    public void add(T number) {
        this.number += number;
    }

    public void subtract(T number) {
        this.number -= number;
    }

}

这不起作用和抛出以下异常：

This won't work and throws the following exception:

对于参数类型（T，T），运算符+ =未定义

The operator += is undefined for the argument type(s) (T, T)

这是因为你不能将该运算符用于对象，也只能用于原始值。

This is because you can't use that operator for objects, and only on primitive values.

我的问题是如何在不知道确切类型的情况下获取给定对象的原始值，只知道它扩展了数字？

My question is how can I get the primitive value of the given object without knowing it's exact type, but just knowing it extends Number?

推荐答案

T总是扩展Object，而不是原始的。您可以使用instanceof然后强制转换为扩展Number的对象。之后 - 如果对象表示基元 - 您可以使用自动拆箱或使用显式转换来使用它。没有办法解决这个问题。

T always extends Object, never a primitive. You can use instanceof and then cast to the object that extends Number. After that - if the object represents a primitive - you can use it using auto unboxing or using an explicit conversion. There is no way around this.

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