问题描述
当我反向遍历一个ArrayList我得到一个IndexOutOfBoundsException异常。我试图做向前迭代并没有问题。我希望,知道有列表中的五行。在code是如下:
When I reverse iterate over an ArrayList I am getting a IndexOutOfBoundsException. I tried doing forward iteration and there is no problem. I expect and know that there are five elements in the list. The code is below:
Collection rtns = absRtnMap.values();
List list = new ArrayList(rtns);
Collections.sort(list);
for(int j=list.size();j>0;j=j-1){
System.out.println(list.get(j));
}
向前迭代 - 这是工作正常,但对我来说没有用处:
Forward iteration - which is working fine, but not useful for me:
for(int j=0;j<list.size();j++){
System.out.println(list.isEmpty());
System.out.println(list.get(j));
} // this worked fine
错误:
Exception in thread "Timer-0" java.lang.IndexOutOfBoundsException: Index: 3, Size: 3
at java.util.ArrayList.RangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at model.Return.getReturnMap(Return.java:61)
at controller.Poller$1.run(Poller.java:29)
at java.util.TimerThread.mainLoop(Unknown Source)
at java.util.TimerThread.run(Unknown Source)
此外,如果任何人反向迭代更好成语知道我会很乐意去尝试了这一点。
Also if anyone knows of a better idiom for reverse iteration I would be happy to try that out.
推荐答案
在启动迭代则为list.size() - 1
因为数组(或 ArrayList的
)元素从0到1小于列表的大小编号。这是一个相当标准的成语:
Start the iteration at list.size() - 1
because array (or ArrayList
) elements are numbered from 0 up through 1 less than the size of the list. This is a fairly standard idiom:
for(int j = list.size() - 1; j >= 0; j--){
// whatever
}
请注意,你向前迭代的作品,因为它停止的前的达到则为list.size()
。
Note that your forward iteration works because it stops before reaching list.size()
.
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