面试：为集合集合设计迭代器 [英] Interview: Design an iterator for a collection of collections

问题描述

在java中设计集合集合的迭代器。迭代器应该隐藏嵌套，允许您遍历属于所有集合的所有元素，就像您使用单个集合一样。

Design an iterator for a collection of collections in java. The iterator should hide the nesting, allowing you to iterate all of the elements belonging to all of the collections as if you were working with a single collection

推荐答案

这是一个可能的实现。注意，我离开remove（）未实现：

Here is a possible implementation. Note that I left remove() unimplemented:

public class MultiIterator <T> implements Iterator<T>{

    private Iterator<? extends Collection<T>> it;
    private Iterator<T> innerIt;
    private T next;
    private boolean hasNext = true;

    public MultiIterator(Collection<? extends Collection<T>> collections) {
        it = collections.iterator();    
        prepareNext();
    }

    private void prepareNext() {
        do {
            if (innerIt == null || !innerIt.hasNext()) {
                if (!it.hasNext()) {
                    hasNext = false;
                    return;
                } else
                    innerIt = it.next().iterator();
            }
        } while (!innerIt.hasNext());

        next = innerIt.next();
    }

    @Override
    public boolean hasNext() {
        return hasNext;
    }

    @Override
    public T next() {
        if (!hasNext)
            throw new NoSuchElementException();
        T res = next;
        prepareNext();
        return res;
    }

    @Override
    public void remove() {
        //TODO
    }

}

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