如何防止迭代器列表发生突变？

如何解决如何防止迭代器列表发生突变？

我想避免其他人更改迭代器 tests 的输入列表。我只希望其他人在 tests 的深层副本上运行。

如何在 Java 中实现这一点？

这是一个示例，显示了突变对 tests 的影响。两部分都是对输入进行排序。但是第二部分没有什么可排序的，因为第一部分的变异将迭代器迭代到了最后。

您可以在此处在线运行以下示例： https://onlinegdb.com/NC4WzLzmt


import java.util.*;

public class ImmutableExample {
    public static void main(String[] args) {

        System.out.println("sort on demand");

        List<Iterator<Integer>> mutableTests = Arrays.asList(
                Arrays.asList(1,2).iterator(),Arrays.asList(0).iterator(),Collections.emptyIterator()
        );

        List<Iterator<Integer>> tests = Collections.unmodifiableList(mutableTests);

        MergingIterator mergingIterator = new MergingIterator(tests);
        while (mergingIterator.hasNext()) {
            System.out.println(mergingIterator.next());
        }

        System.out.println("sort all at once");

        /*       uncomment the following will see the same result:*/
//        tests = Arrays.asList(
//                Arrays.asList(1,//                Arrays.asList(0).iterator(),//                Collections.emptyIterator()
//        );

        MergeKSortedIterators sol = new MergeKSortedIterators();
        Iterable<Integer> result = sol.mergeKSortedIterators(tests);

        for (Integer num : result) {
            System.out.println(num);
        }


    }
}

class PeekingIterator implements Iterator<Integer>,Comparable<PeekingIterator> {
    Iterator<Integer> iterator;
    Integer peekedElement;
    boolean hasPeeked;

    public PeekingIterator(Iterator<Integer> iterator) {
        this.iterator = iterator;
    }


    public boolean hasNext() {
        return hasPeeked || iterator.hasNext();
    }

    public Integer next() {
        int nextElem = hasPeeked ? peekedElement : iterator.next();
        hasPeeked = false;
        return nextElem;
    }

    public Integer peek() {
        peekedElement = hasPeeked ? peekedElement : iterator.next();
        hasPeeked = true;
        return peekedElement;
    }

    @Override
    public int compareTo(PeekingIterator that) {
        return this.peek() - that.peek();
    }


}


class MergingIterator implements Iterator<Integer> {
    Queue<PeekingIterator> minHeap;

    public MergingIterator(List<Iterator<Integer>> iterators) {
//        minHeap = new PriorityQueue<>((x,y) -> x.peek().compareTo(y.peek()));
        minHeap = new PriorityQueue<>();
        for (Iterator<Integer> iterator : iterators) {
            if (iterator.hasNext()) {
                minHeap.offer(new PeekingIterator(iterator));
            }
        }
    }

    public boolean hasNext() {
        return !minHeap.isEmpty();
    }

    public Integer next() {
        PeekingIterator nextIter = minHeap.poll();
        Integer next = nextIter.next();
        if (nextIter.hasNext()) {
            minHeap.offer(nextIter);
        }
        return next;
    }
}

class MergeKSortedIterators {


    public Iterable<Integer> mergeKSortedIterators(List<Iterator<Integer>> iteratorList) {
        List<Integer> result = new ArrayList<>();
        if (iteratorList.isEmpty()) {
            return result;
        }

        PriorityQueue<PeekingIterator> pq = new PriorityQueue<>();

        for (Iterator<Integer> iterator : iteratorList) {
            if (iterator.hasNext()) {
                pq.add(new PeekingIterator(iterator));
            }
        }

        while (!pq.isEmpty()) {
            PeekingIterator curr = pq.poll();
//            result.add(curr.peek());
// cannot use this one as hasNext() checks on `hasPeeked`
            result.add(curr.next());
            if (curr.hasNext()) {
                pq.add(curr);
            }
        }

        return result;
    }


}