运行时错误 Java [英] Runtime error Java

问题描述

我是 Java 初学者，我有一个运行时错误问题.我已经正确回答了，但是我并不完全理解答案背后的概念.谁能解释一下为什么B是这个问题的正确答案，谢谢:

I am a beginner in Java and I have a run time error question. I have answered it correctly, however I do not completely understand the concept behind the answer. Could someone please explain why B is the right answer to the question, thank you:

考虑以下声明:

private ArrayList<String> list;
...
public void printAll()
{
int index = 0;
while (index < list.size) {
index = index + 1;
System.out.println(list.get(index));
   }
}

假设 list 不为 null，关于调用 printAll()，下列哪一项是正确的?

Assuming that list is not null, which one of the following is true about invocations of printAll()?

a)仅当列表为空时才会发生运行时错误.

a)A run-time error occurs only if the list is empty.

b) 仅当列表不为空时才会发生运行时错误.

b)A run-time error occurs only if the list is not empty.

c) 永远不会发生运行时错误.

c)A run-time error never occurs.

d) 总是会发生运行时错误.

d)A run-time error always occurs.

e)只要列表的长度为偶数，就会发生运行时错误

e)A run-time error occurs whenever the list has an even length

推荐答案

while (index < list.size) {
 index = index + 1;
 System.out.println(list.get(index));
}

这里 index 在访问列表之前增加.所以它每次都提前读取一个元素.所以当列表不为空时运行时出错.

Here index is incremented before accessing the list. So it reads one element ahead everytime. So run-time error when the list is not empty.

如果列表为空，则条件 while (index 将失败，因此将永远不会执行导致运行时错误的循环代码.

If the list is empty then the condition while (index < list.size) will fail and hence the loop code that causes the run-time error will never be executed.

虽然与您的问题无关，但正确的代码是在阅读后增加 index :

Although not relevant to your question, the correct code would be to increment the index after reading:

while (index < list.size) {
 System.out.println(list.get(index));
 index = index + 1;
}

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