code: @SuppressWarnings("unchecked")
  	public static <T> HashSet<T> newHashSet(T... elements) {
  		return Sets.newHashSet(elements);
  	}
docs: 根据等号左边的类型，构造类型正确的HashSet, 并初始化元素.
  
  @see com.google.common.collect.Sets#newHashSet(Object...)