如何修复此错误 java.util.ConcurrentModificationException [英] How can I fix this error java.util.ConcurrentModificationException

问题描述

我在以下行中收到错误消息.我正在做添加到 jsonarray 的过程.请帮帮我.

I get an error on the following line. I'm doing the process of adding to the jsonarray. Please help me.

jsonArr=new JSONArray();
if(req.getSession().getAttribute("userses")!=null){
    String name=(req.getParameter("name")==null?"":to_EnglishName(req.getParameter("name").toUpperCase()));
    if(!name.equals("")){
        for(Book c:GlobalObjects.bookList){
            if(c.getBookName().startsWith(name)){
                    jsonObjec=new JSONObject();
                    jsonObjec.put("label",c.getBookName());
                    jsonObjec.put("value", c.getId());
                    jsonArr.add(jsonObjec);//java.util.ConcurrentModificationException
            }
        }
    }
}
jsonArr.write(res.getWriter());

推荐答案

这是我在重新编程时经常遇到的错误.此异常的原因或细节非常清楚.不允许在迭代时修改集合(您正在添加新元素).至少语法 for 不支持这样做.

This is an error I often met while reprogramming. the reason or detail of this exception are pretty clear. it is unallowed to modify the collection(you are adding a new element) while it is being iterated. At least the syntax for DO NOT support do that.

要解决您的问题，我认为有两种方法很简单.

To fix your problem, there have two way I think it is simple.

1).与使用 for 语句循环相比，更好的方法是使用迭代器来避免 ConcurrentModificationException.

1). rather than using for statement to loop over, the better way is to use iterator to avoid ConcurrentModificationException.

    Iterator<Book> iterator = bookList.iterator();
    while(iterator.hasNext()){
      Book c = iterator.next();
      if(c.getBookName().startsWith(name)){
                jsonObjec=new JSONObject();
                jsonObjec.put("label",c.getBookName());
                jsonObjec.put("value", c.getId());
                jsonArr.add(jsonObjec);
        }
    }

2).循环时，不要添加.

2). while looping it, don't add it.

     List list = new ArrayList<>();
     for(Book c:GlobalObjects.bookList){
        if(c.getBookName().startsWith(name)){
                jsonObjec=new JSONObject();
                jsonObjec.put("label",c.getBookName());
                jsonObjec.put("value", c.getId());
                list.add(jsonObjec);//java.util.ConcurrentModificationException
        }
     }
     jsonArr.addAll(list);

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