Question

我正在尝试用GUI创建一个java应用程序。我正在编写一个代码，我想让用户更改一些数据并将这些更改保存在文本文件中。在这之前我想删除从列表中更改的旧数据，然后用最后一次更改重写新数据。如果我想错过任何你想看的课，请告诉我，我会尽快将它放在网上< / p>

这是我的

    public void saveChanges(footBall Player, String name, String level,
        int[] scores, int footSize) {

    try {
        if (CompetitorsList.size() != 0) {
            for (Competitors C : CompetitorsList) {

                if (C instanceof footBall) {
                    String Number = Player.playerNumber + "";
                    if (C.getPlayerNumberAsString().equals(Number)) {
                        System.out.println("c");

 //the error hit me here when i try to remove the object from the list the exception error is       java.util.ConcurrentModificationException 
                        CompetitorsList.remove(C);

                    }

                }
            }

            Name NewName = new Name(name);
            System.out.println("Please get in2");
            footBall NewPlayer = new footBall(Player.playerNumber, scores,
                    level, footSize, NewName);

            CompetitorsList.add(NewPlayer);

            SaveOnFile();
        } else {
            System.out.println("No List");
        }

    } catch (Exception ex) {
        System.out.print("testing4");
        System.out.print("something wrong" + ex);
    }

}

这是SaveOnFile方法： public void SaveOnFile（）{

    String scoresInString;
    FileWriter fw;
    try {

        fw = new FileWriter("footBall");

        for (Competitors C : CompetitorsList) {
            if (C instanceof footBall) {
                footBall Scores = new footBall();
                scoresInString = Scores.returnScoreAsString(C.scores);
                fw.write(C.playerNumber + ", " + C.name.getFullName()
                        + ", " + C.level + ", " + scoresInString + ","
                        + ((footBall) C).footSize() + "\n");
                fw.write("\r\n");
            }

        }

        fw.close();

    }
    // message and stop if file not found
    catch (FileNotFoundException fnf) {
        System.out.println("File not found ");
        System.exit(0);
    }
    // stack trace here because we don't expect to come here
    catch (IOException ioe) {
        ioe.printStackTrace();
        System.exit(1);
    }
}

Answer 1

对集合调用remove（）会使所有活动迭代器无效。相反，您必须使用Iterator.remove（）方法：

for(Iterator<Competitors> it = CompetitorsList.iterator(); it.hasNext(); ) {
    Competitors C = it.next();
    if(C instanceof ...) {
        if(C.getPlayerNumberAsString().equals(Number))
            it.remove();
    ...

这样，iterator（）知道集合是如何更改的，否则将无法实现，因为ArrayList不会跟踪它生成的迭代器。

Answer 2

或者，如果要使用相同的“for-next”语法而不是更改为Iterator语法，请将要删除的所有对象收集到临时集合中。 e.g。

ArrayList<Competitors> removeThese = new ArrayList<Competitors>();
for (Competitors C : CompetitorsList) {
   if (wantToRemove(C))  // your number logic goes here...
      removeThese.add(C);
}
CompetitorsList.removeAll(removeThese);

java.util.ConcurrentModificationException异常错误

2 个答案: