import java.nio.file.FileTreeWalker.Event; //导入依赖的package包/类
private void fetchNextIfNeeded() {
    if (next == null) {
        FileTreeWalker.Event ev = walker.next();
        while (ev != null) {
            IOException ioe = ev.ioeException();
            if (ioe != null)
                throw new UncheckedIOException(ioe);

            // END_DIRECTORY events are ignored
            if (ev.type() != FileTreeWalker.EventType.END_DIRECTORY) {
                next = ev;
                return;
            }
            ev = walker.next();
        }
    }
}
 

import java.nio.file.FileTreeWalker.Event; //导入依赖的package包/类
@Override
public Event next() {
    if (!walker.isOpen())
        throw new IllegalStateException();
    fetchNextIfNeeded();
    if (next == null)
        throw new NoSuchElementException();
    Event result = next;
    next = null;
    return result;
}