由于某种原因,我得到了一个带有以下代码的UnsupportedOpeationException
。在调试器中对其进行检查,它看起来像我正在调用remove()
的对象是一个列表。
// to optimize, remove totalSize. After taking an item from lowest, if lowest is empty, remove it from `lists`
// lists are sorted to begin with
public static <T extends Comparable<? super T>> List<T> merge(Set<List<T>> lists) {
List<T> result = new ArrayList<T>();
HashMap<List<T>, Integer> location = new HashMap<List<T>, Integer>();
int totalSize = 0; // every element in the set
for (List<T> l : lists) {
location.put(l, 0);
totalSize += l.size();
}
boolean first;
List<T> lowest = lists.iterator().next(); // the list with the lowest item to add
int index;
while (result.size() < totalSize) { // while we still have something to add
first = true;
for (List<T> l : lists) {
if (! l.isEmpty()) {
if (first) {
lowest = l;
}
else if (l.get(location.get(l)).compareTo(lowest.get(location.get(lowest))) <= 0) {
lowest = l;
}
}
}
index = location.get(lowest);
result.add(lowest.get(index));
lowest.remove(index); //problem here
}
return result;
}
异常(exception):
Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.AbstractList.remove(Unknown Source)
at interview.questions.MergeLists.merge(MergeLists.java:72)
at interview.questions.MergeLists.main(MergeLists.java:32)
为什么会这样呢?
最佳答案
您收到的List
的基础实现很有可能是固定长度的,例如 Arrays#asList
创建的。