public static <E> Set<E> intersectionView(final Set<E> set1, final Set<?> set2) {
		return Sets.intersection(set1, set2);
	}
public static < E > Set < E > intersectionView ( final Set < E > set1 , final Set < ? > set2 ) { return Sets . intersection ( set1 , set2 ) ; }
set1, set2的交集（同时在set1和set2的对象）的只读view，不复制产生新的Set对象.

如果尝试写入该View会抛出UnsupportedOperationException