Java -如何获得交错迭代器/集合

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class InterleavedIteratorExample {
    public static void main(String[] args) {
        List<List<Integer>> nestedList = new ArrayList<>();
        nestedList.add(List.of(1, 2, 3));
        nestedList.add(List.of(4, 5));
        nestedList.add(List.of(6, 7, 8, 9));

        Iterator<Integer> interleavedIterator = new InterleavedIterator<>(nestedList);

        while (interleavedIterator.hasNext()) {
            System.out.print(interleavedIterator.next() + " ");
        }
    }
}

class InterleavedIterator<T> implements Iterator<T> {
    private final List<List<T>> nestedList;
    private int outerIndex;
    private int innerIndex;

    public InterleavedIterator(List<List<T>> nestedList) {
        this.nestedList = nestedList;
        this.outerIndex = 0;
        this.innerIndex = 0;
    }

    @Override
    public boolean hasNext() {
        while (outerIndex < nestedList.size() && innerIndex >= nestedList.get(outerIndex).size()) {
            outerIndex++;
            innerIndex = 0;
        }
        return outerIndex < nestedList.size();
    }

    @Override
    public T next() {
        T element = nestedList.get(outerIndex).get(innerIndex);
        innerIndex++;
        return element;
    }
}