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

问题描述

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大家好。
我正在制作一个词汇应用程序，我需要创建一个
List< String> （或ArrayList）。为此，我创建了以下代码片段（仅作为示例）：

 列表与LT;字符串> tempSOLUTION = new ArrayList< String>（）; 
 String temp =abc123; 
 tempSOLUTION.add（temp）; 
  

我也尝试了以下内容：

< pre class =lang-java prettyprint-override> tempSOLUTION.add（new String（temp））;


他们都将项目添加到列表中，但在调试时，我发现它的数组有12个对象，如下所示：

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

我的问题是我不能拥有那些null项，因为这个新列表是 HashableMap< String> 的键，所以任何更改都会导致异常，因为密钥不存在。

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

如何在不创建所有空项目的情况下将项目添加到列表中？

搜索完成后，我找到了如何删除这些空项的答案，其中包括：

  tempSOLUTI ON.removeAll（Collections.singleton（空））; 
  

但它不能用于我的目的。

提前致谢。

解决方案

您可能正在使用调试器查看其内部数组。那没关系;它只是一个实现细节。

重要的是通过其公共API可见的内容。换句话说，什么调用 size（）（等等）告诉你。 （如果你的代码示例中没有返回 1 ，那么会发生一些奇怪的事情！）

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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);

I've also tried the following:

tempSOLUTION.add(new String(temp));

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]

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.

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

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

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

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

But it does not work for my purpose.

Thanks in advance.

解决方案

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

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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