ArrayList 自动添加空项 [英] ArrayList automatically adding null items

问题描述

大家好.我正在制作一个词汇应用程序，我需要在其中创建一个List(或 ArrayList).为此，我创建了以下代码段(仅作为示例):

Hello everyone. I'm making a vocabulary App, in which I need to create a List<String> (or ArrayList). To do so, I've created the following piece of code (just an example):

List<String> tempSOLUTION = new ArrayList<String>();
String temp = "abc123";
tempSOLUTION.add(temp);

我还尝试了以下方法:

tempSOLUTION.add(new String(temp));

他们都把item加入到list中，但是调试的时候发现它的array有12个对象，如下:

Both of them add the item to the list, but while debugging, I find that it's array has 12 objects, which are the following:

[abc123, null, null, null, null, null, null, null, null, null, null, null]

我的问题是我不能拥有那些空项目，因为这个新列表是 HashableMap 上的键，所以任何更改都会导致异常，因为键不存在.

My problem is that I cannot have those null items, as this new list is the key on a HashableMap<String>, so any change will cause an exception, as the key would NOT exist.

使用调试器的列表 (tempSOLUTION) 详细信息的屏幕截图:http://www.pabloarteaga.es/stackoverflow.jpg

Screenshot of the list (tempSOLUTION) details using the debugger: http://www.pabloarteaga.es/stackoverflow.jpg

如何在不创建所有这些空项目的情况下将项目添加到列表中?

How can I add an item to the list without creating all those null items?

搜索后，我找到了一个关于如何删除这些空项目的答案，即:

After having searched, I found an answer on how to remove these null items, which is:

tempSOLUTION.removeAll(Collections.singleton(null));

但它不适合我的目的.

提前致谢.

推荐答案

您可能正在使用调试器查看其内部数组.没关系；这只是一个实现细节.

You're probably looking at its internal array with the debugger. That doesn't matter; it's just an implementation detail.

重要的是通过其公共 API 可见的内容.换句话说，对 size()(等等)的调用会告诉你什么.(如果在您的代码示例中没有返回 1，那么就会发生一些奇怪的事情！)

What matters is what's visible through its public API. In other words, what calls to size() (and so on) tell you. (And if that doesn't return 1 in your code example, then something weird is going on!)

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