小编Arn*_*rno的帖子

Guava Sets.difference#isEmpty()行为

我不理解Guava的集合的行为#isremp()方法的区别:

  public static <E> SetView<E> difference(final Set<E> set1, final Set<?> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    final Predicate<Object> notInSet2 = Predicates.not(Predicates.in(set2));
    return new SetView<E>() {
      @Override public Iterator<E> iterator() {
        return Iterators.filter(set1.iterator(), notInSet2);
      }
      @Override public int size() {
        return Iterators.size(iterator());
      }
      @Override public boolean isEmpty() {
        return set2.containsAll(set1);
      }
      @Override public boolean contains(Object element) {
        return set1.contains(element) && !set2.contains(element);
      }
  };
}

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更确切地说,我不明白如何set2.containsAll(set1);使用它的结果isEmpty().

举个例子: