如何实现此FilteringIterator？

您将需要使迭代器成为有状态的。缓存您从中检索到的最后一个值，

hasNext

next

private boolean hasCached;private T cached;public boolean hasNext() {   if ( hasCached ) return true;   //iterate until you find one and set hasCached and cached}public T next() {   if ( hasCached ) {      hasCached = false;      return cached;   }   //iterate until next matches}