修改作为method-parameter传递的数组 [英] Modify an array passed as a method-parameter

问题描述

假设我有一个int数组，我想修改它。我知道我不能将新数组分配给作为参数传递的数组：

Suppose I have an int-array and I want to modify it. I know that I cannot assign a new array to array passed as parameter:

public static void main(String[] args)
{
    int[] temp_array = {1};
    method(temp_array);
    System.out.println(temp_array[0]); // prints 1
}
public static void method(int[] n)
{
    n = new int[]{2};
}

我可以修改它：

public static void main(String[] args)
{
    int[] temp_array = {1};
    method(temp_array);
    System.out.println(temp_array[0]); // prints 2
}
public static void method(int[] n)
{
    n[0] = 2;
}

然后，我尝试将任意数组分配给作为参数传递的数组 clone（）：

Then, I tried to assign an arbitrary array to the array passed as parameter using clone():

public static void main(String[] args)
{
    int[] temp_array = {1};
    method(temp_array);
    System.out.println(temp_array[0]); // prints 1 ?!
}
public static void method(int[] n)
{
    int[] temp = new int[]{2};
    n = temp.clone();
}

现在，我想知道为什么它在上一个例子中打印1而我只是使用 clone（）复制数组，它只是复制值而不是引用。你可以帮我解释一下吗？

Now, I wonder why it prints 1 in last example while I'm just copying the array with clone() which it's just copying the value not the reference. Could you please explain that for me?

编辑：有没有办法复制一个数组到对象而不更改引用？我的意思是让最后一个例子打印 2 。

Is there a way to copy an array to object without changing the reference? I mean to make last example printing 2.

推荐答案

你的例子1在问题的上下文中，3和几乎是相同的 - 您正在尝试为 n 分配一个新值（这是对按值传递的数组的引用）。

Your examples 1 and 3 are virtually the same in context of the question - you are trying to assign a new value to n (which is a reference to an array passed by value).

您克隆 temp 数组的事实并不重要 - 所有这一切都是创建<$的副本c $ c> temp 然后将其分配给 n 。

The fact that you cloned temp array doesn't matter - all it did was create a copy of temp and then assign it to n.

为了将值复制到传递到方法方法的数组中，您可能需要查看： System.arraycopy

In order to copy values into array passed into your method method you might want to look at:System.arraycopy

这一切当然取决于你的的大小n 数组和您在方法方法中创建的数组。

It all, of course, depends on the sizes of your n array and the one you create inside method method.

假设它们都有相同的长度，例如，你会这样做：

Assuming they both have the same length, for example, you would do it like that:

public static void main(String[] args)
{
    int[] temp_array = {1};
    method(temp_array);
    System.out.println(temp_array[0]);
}
public static void method(int[] n)
{
    int[] temp = new int[]{2};
    System.arraycopy(temp, 0, n, 0, n.length); 
    // or System.arraycopy(temp, 0, n, 0, temp.length) - 
    // since we assumed that n and temp are of the same length
}

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