Java在foreach中修改元素 [英] Java Modifying Elements in a foreach

问题描述

我正在自学 Java；因此下面的代码除了学习/测试之外没有其他功能.

I'm learning Java on my own; and therefore the code below has no function other than for learning/testing.

本质上，我试图在 foreach 循环中修改整数数组的元素(即，将它们减半).

Essentially I'm trying to modify the elements of an Integer array (namely, halving them) whilst in a foreach loop.

我应该注意，我没有重新排序、添加或删除元素；只需更改它们的值.

I should note that I'm not re-ordering, adding, or deleting elements; simply changing their values.

这是我的代码:

Logger.describe("Now copying half of that array in to a new array, and halving each element");
Integer[] copyArray = new Integer[DEFAULT_SAMPLE_SIZE / 2];     
System.arraycopy(intArray, 0, copyArray, 0, DEFAULT_SAMPLE_SIZE / 2);
for (Integer x : copyArray) x /= 2;
Logger.output(Arrays.deepToString(copyArray));

然而，原来的数组(intArray)是这样的:

However, the original array (intArray) is this:

[47, 31, 71, 76, 78, 94, 66, 47, 73, 21]

copyArray 的输出是:

And the output of copyArray is:

[47, 31, 71, 76, 78]

因此，尽管数组的大小减半，但元素(整数)的值并没有减半.那么我做错了什么?

So although the array has been halved in size, the elements (Integers) haven't also been halved in value. So what am I doing wrong?

谢谢

推荐答案

你不能在 foreach 循环中这样做.

You can't do that in a foreach loop.

for (int i=0; i<copyArray.length;i++)
    copyArray[i] /= 2;

否则您不会将其分配回数组.顺便说一下，Integer 对象是不可变的，因此不能修改它们(尽管创建新的).

Else you are not assigning it back into the array. Integer objects are immutable by the way so can't modify them (creating new ones though).

从评论更新:请注意，有一些事情正在发生，例如自动装箱/拆箱，大致如下:

Updated from comment: Beware though that there are a few things going on, autoboxing/unboxing for example, roughly:

copyArray[i] = Integer.valueOf(copyArray[i].intValue()/2);

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