无法在 for 循环中向 ArrayList 添加元素

问题描述：

我目前遇到无法在 Android 应用开发中运行以下代码的问题.

I am currently having the problem of not able to run the following code in Android app development.

import java.util.ArrayList;

public class Test extends FragmentActivity {

ArrayList<String> random;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
        for (int a=0; a<11; a++){
        random.add("a");
    }
            }
    }

我知道上面的代码做了无用的操作，但这是从我在 JAVA 中的 for 循环代码中的问题简化的.我从错误日志中得到了这个错误，未处理的事件循环异常".谁能指出我做错了什么?

I know the above code does useless action but that is simplified from my problem in the for loop code in JAVA. And I got this error from the error log, "unhandled event loop exception". Can anyone point out that what I am doing wrong please?

答

至少有两个问题(我怀疑).

There are at least two problems (I suspect).

首先，您得到一个 NullPointerException，因为您没有使用引用实际对象的值初始化 random.

First, you're getting a NullPointerException because you're not initializing random with a value referring to an actual object.

接下来，你的语法在这里很糟糕:

Next, your syntax is bad here:

for (int a=0; a<11; a++);

您的代码只是向 random 添加了一个元素 - 它相当于:

Your code is only adding a single element to random - it's equivalent to:

for (int a=0; a<11; a++)
{
}
random.add("a");

我非常怀疑这就是您的意图.我的猜测是你想要这个:

I very much doubt that that's what you were intending. My guess is that you wanted this instead:

for (int a=0; a<11; a++)
{
    random.add("a");
}

无法在 for 循环中向 ArrayList 添加元素

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