运行时错误的Ja​​va [英] Runtime error Java

问题描述

我在Java初学者，我有一个运行时错误的问题。我已经回答正确了，但我不完全理解的答案背后的概念。可能有人请解释为什么B是正确答案的问题，谢谢：

考虑以下声明：

 私人的ArrayList＆LT;串GT;清单;
...
公共无效printAll（）
{
INT索引= 0;
而（指数＆LT;则为list.size）{
指数=指数+ 1;
的System.out.println（list.get（指数））;
   }
}
 

假设列表不为空，下列哪一个是真实的约printAll（）？

的调用

a）仅当列表为空时，会发生运行时错误。

B）仅当列表不为空，出现运行时错误。

c）一个运行时错误永远不会发生。

d）一个运行时错误总是发生。

E）每当列表有偶数长度发生运行时错误

解决方案

 而（指数＆LT;则为list.size）{
 指数=指数+ 1;
 的System.out.println（list.get（指数））;
}
 

下面首页递增的前的访问列表。因此，它读取一个元素提前每次。因此，运行时错误当列表不是空的。

如果列表为空则条件而（指数＆LT;则为list.size）将失败，因此环code，导致运行时错误将永远不会被执行。

虽然您的问题不相关的，正确的code将递增首页读后：

 而（指数＆LT;则为list.size）{
 的System.out.println（list.get（指数））;
 指数=指数+ 1;
}
 

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:

Consider the following declarations:

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

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

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

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

c)A run-time error never occurs.

d)A run-time error always occurs.

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

解决方案

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

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.

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.

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;
}

这篇关于运行时错误的Ja​​va的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！