ListIterator 和并发修改异常的问题 [英] Problems with ListIterator and Concurrent Modification Exception

问题描述

我有两个 ArrayList，每个都包含一定大小的块:blockList、eraseList.块是具有两个字段的对象:开始和结束.我需要从另一组块中减去一组块.

I have two ArrayLists, each holding blocks of certain size: blockList, eraserList. Blocks are objects with two fields: start and end. I need to subtract one set of blocks from the other set of blocks.

我必须遍历擦除器列表并从它们重叠的块列表中擦除"块.因此我的代码看起来像:

I must walk through the eraserList and "erase" blocks out of the blockList where they overlap. Thus my code looks like:

 void eraseBlocks (Arrylist<Blocks> blockList, ArrayList<Blocks> eraserList) {
    ListIterator<Blocks> it = blockList.listIterator();

    for (Blocks eraser: eraserList) {
        while (it.hasNext()) {
            Blocks block= it.next();
            if ((eraser.start <= block.start) && (eraser.end >= block.end))
                 blockList.remove(block);
            else if ((eraser.start <= block.start) && (eraser.end < block.end)){
                 block.set(start, eraser.end);
            else if () {
                        ...
                 //more code for where the eraser partially erases the beginning, end, or splits the block
                 //if statements call the .add(), .set(), and remove() methods on the blockList.
                        ...
                  }
            }
        }

我不明白为什么我会收到并发修改异常.我从不修改擦除器列表.

I don't understand why I am getting a Concurrent Modification Exception. I never modify the eraserList.

我正在尝试修改在Block block = it.next();"中分配的块对象陈述.我还通过在列表中删除或添加块来修改 blockList.我认为 ListIterator 的全部意义在于它允许您修改、添加或减去您正在浏览的列表.

I am trying to modify the block object that is assigned in the "Block block = it.next();" statement. I am also modifying the blockList by removing or adding blocks to the list. I thought the whole point of the ListIterator was that it allowed you to modify, add, or subtract a list you are walking through.

失败跟踪指向块擦除器 = it.next();作为绘制异常的线条，但我不知道那是在告诉我什么.

The Failure Trace points to the Blocks eraser = it.next(); as the line drawing the exception, but I don't know what that is telling me.

谁能帮我弄清楚我做错了什么?

Can anyone help me figure out what I am doing wrong?

谢谢！

推荐答案

是的，ListIterator 旨在允许修改列表.但是您没有使用 ListIterator 的 remove() 方法，而是直接操作底层列表本身.

Yes, ListIterator is designed to allow the modification of the list. But you are not using the remove() method of the ListIterator, but directly manipulate the underlying list itself.

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