Java传播运算符 [英] Java spread operator

问题描述

我不确定我在这里使用的词汇，如果我错了，请纠正我。

I am not sure of the vocabulary I am using here, please correct me if I'm wrong.

在Javascript中，我有以下代码：

In Javascript, I had the following code:

let args = [1,2,3];

function doSomething (a, b, c) {
    return a + b + c;
}

doSomething(...args);

正如您所见，当致电 doSomething ，我可以使用 ... spread运算符，以便将我的参数转换为 1,2,3 。

As you can see, when calling doSomething, I am able to use the ... spread operator in order to "transform" my arguments into 1, 2, 3.

现在，我正在尝试用Java做同样的事情。

Now, I'm trying to do the same thing with Java.

假设我有一个 Foo 类：

public class Foo {
    public int doSomething (int a, int b, int c) {
        return a + b + c;
    }
}

现在我要拨打 doSomething ：

int[] args = {1, 2, 3};

我想使用像 doSomething（... args）之类的东西而不是调用 doSomething（args [0]，args [1]，args [2]）。

I'd like to use something like doSomething (...args) instead of calling doSomething(args[0], args[1], args[2]).

我看到这在函数声明中是可行的，但我不想改变这样一个函数的实现。

I saw that this is possible in the declaration of functions, but I'd like not to change the implementation of such a function.

推荐答案

Java语言不提供运算符来执行此操作，但其类库可以提供您所需的功能。

Java language does not provide an operator to do this, but its class library has a facility to do what you need.

[来自OP的评论] Foo的开发者可以自己选择doSomething函数的参数数量。然后我就可以构造一个包参数并将其注入方法中。

[from OP's comment] The developer of Foo could choose himself the number of arguments that function doSomething takes. I would then be able to construct a "bag" of arguments and inject it in the method.

使用反射API ，这就是它的用途。它要求您在数组中打包参数。还需要做很多额外的工作，包括包装/解包单个方法参数和方法结果，但是你可以在运行时检查签名，构造一个数组，然后调用方法。

Use reflection API, this is what it is for. It requires you to package arguments in an array. There is a lot of extra work required, including wrapping/unwrapping individual method arguments, and method result, but you can check the signature at run-time, construct an array, and call the method.

class Test {
    public static int doSomething(int a, int b, int c) {
        return a + b + c;
    }
    // This variable holds method reference to doSomething
    private static Method doSomethingMethod;
    // We initialize this variable in a static initialization block
    static {
        try {
            doSomethingMethod = Test.class.getMethod("doSomething", Integer.TYPE, Integer.TYPE, Integer.TYPE);
        } catch (Exception e) {
        }
    }
    public static void main (String[] ignore) throws java.lang.Exception {
        // Note that args is Object[], not int[]
        Object[] args = new Object[] {1, 2, 3};
        // Result is also Object, not int
        Object res = doSomethingMethod.invoke(null, args);
        System.out.println(res);
    }
}

以上代码打印6（演示）。

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