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);
}

它扔了

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？还是一个小虫......

Answer 1

SetView是这些集合的交集的视图,而不是副本.来自番石榴文档:

可以由其他集支持的集合的不可修改的视图; 此视图将随后备集的变化而变化.

因此,当您调用set1.removeAll(x)并传入视图时,您实际上是在尝试从set1循环部分自身时删除.这就是原因ConcurrentModificationException.

要实现您想要做的事情,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);