如何在线程"main"java.util.ConcurrentModificationException中修复Exception

Question

我有2个HashMap<Integer,Point3D>对象名称positiveCoOrdinate and negativeCoOrdinates.

我正在检查PositiveCoOrdinates以下条件.如果它满足相应的点添加negativeCoOrdinates和删除positiveCoOrdinates.

  HashMap<Integer, Point3d> positiveCoOrdinates=duelList.get(1);
  HashMap<Integer, Point3d> negativecoOrdinates=duelList.get(2);
  //condition
  Set<Integer> set=positiveCoOrdinates.keySet();
    for (Integer pointIndex : set) {
        Point3d coOrdinate=positiveCoOrdinates.get(pointIndex);
        if (coOrdinate.x>xMaxValue || coOrdinate.y>yMaxValue || coOrdinate.z>zMaxValue) {
            negativecoOrdinates.put(pointIndex, coOrdinate);
            positiveCoOrdinates.remove(pointIndex);
        }
    }

添加,删除时间我收到以下错误.

 Exception in thread "main" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
at java.util.HashMap$KeyIterator.next(Unknown Source)
at PlaneCoOrdinates.CoordinatesFiltering.Integration(CoordinatesFiltering.java:167)
at PlaneCoOrdinates.CoordinatesFiltering.main(CoordinatesFiltering.java:179)

对于我的测试,我System.out.println(coOrdinate.x);在If条件内提到了声明.工作正常.

如果我在If条件中添加2行(我上面提到的内容),则会抛出错误.

我怎样才能解决这个问题.

谢谢.

Answer 1

最简单的方法是制作keySet的副本:

  Set<Integer> set= new HashSet<Integer>(positiveCoOrdinates.keySet());

出现此问题的原因是您正在修改positiveCoOrdinates使用Iterator迭代键的方法.

您还可以重构代码并在条目集上使用迭代器.这将是一种更好的方法.

Set<Entry<Integer, Point3d>> entrySet = positiveCoOrdinates.entrySet();

    for (Iterator<Entry<Integer, Point3d>> iterator = entrySet.iterator(); iterator.hasNext();) {
        Entry<Integer, Point3d> entry = iterator.next();
        Point3d coOrdinate = entry.getValue();
        if (coOrdinate.x > xMaxValue || coOrdinate.y > yMaxValue
                || coOrdinate.z > zMaxValue) {
            Integer pointIndex = entry.getKey();
            negativecoOrdinates.put(pointIndex, coOrdinate);
            iterator.remove();
        }
    }