java - com.google.common.collect.Sets.SetView 错误或功能？

Question

你好，我有这段代码:

public static void main(String[] args) {
    Set<Integer> set1 = new HashSet<Integer>();
    Set<Integer> set2 = new HashSet<Integer>();
    set1.add(1);
    set1.add(2);
    set1.add(3);
    set1.add(4);
    set1.add(5);

    set2.add(4);
    set2.add(5);
    set2.add(6);
    set2.add(7);
    set2.add(8);

    SetView<Integer> x = Sets.intersection(set1, set2);
    set1.removeAll(x);
    set2.removeAll(x);
}

它抛出

Exception in thread "main" java.util.ConcurrentModificationException
    at java.util.HashMap$HashIterator.nextEntry(HashMap.java:841)
    at java.util.HashMap$KeyIterator.next(HashMap.java:877)
    at com.google.common.collect.Iterators$7.computeNext(Iterators.java:627)
    at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:141)
    at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:136)
    at java.util.AbstractSet.removeAll(AbstractSet.java:142)
    at com.Main2.main(Main2.java:30)

这是正常的吗？或者一个小错误...

Answer 1

SetView是这些集合的交集的 View ，而不是副本。来自 Guava 文档:

An unmodifiable view of a set which may be backed by other sets; this view will change as the backing sets do.

因此，当您调用 set1.removeAll(x) 并传入 View 时，您实质上是在尝试从 set1 中删除，同时循环其自身的一部分。这就是 ConcurrentModificationException 的原因.

要实现您的目标，请查看 SetView.immutableCopy() .

例如:

SetView<Integer> intersectionView = Sets.intersection(set1, set2);
ImmutableSet<Integer> intersectionCopy = intersectionView.immutableCopy();
set1.removeAll(intersectionCopy);
set2.removeAll(intersectionCopy);