java.lang.IllegalStateException：带有迭代器的null

Question

For some reason, I'm getting java.lang.IllegalStateException: null exception from the method that was working just fine before. I don't think I made any changes on this. It just suddenly stopped working and it doesn't throw an error on every entry, just the one that is 4. in the list. I can't even see anything different on that entry, it has all the properties it's supposed to have.

Iterator<Class> iter = contacts.iterator();

while (iter.hasNext()){
        Class holder = iter.next();
        try {
            if(dateNow.isBefore(holder.getStartDate())){
                iter.remove();
            }if(dateNow.isAfter(holder.getEndDate())){
                iter.remove();
            }else{
                boolean status = checkStatus(holder);
                if(!status){
                    iter.remove();
                }
            }
        }catch (NullPointerException e) {
            //No end-date or start date
            boolean status = checkStatus(holder);
            if(!status){
                iter.remove();
            }
            else if(dateNow.isBefore(holder.getStartDate())){
                iter.remove();
            }
        }
    }

is throwing this error. My only reason to use an iterator is that I can remove items while iterating it.

if(!status){
      iter.remove();
       }

is the spesific line throwing the error, iter.remove() part. status is false, as it should.

thanks for any help.

Answer 1

It looks like you might be trying to remove the same element twice from the iterator.

I suggest changing the logic to:

        if (dateNow.isBefore(holder.getStartDate())) {
            iter.remove();
        } else if (dateNow.isAfter(holder.getEndDate())) { // notice the change here
            iter.remove();
        } else {
            boolean status = checkStatus(holder);
            if(!status){
                iter.remove();
            }
        }

Now, if the first condition is true (and iter.remove() is called), the else clause won't be executed.

I also suggest to avoid the NullPointerException instead of catching it. For example:

    if (holder.getStartDate() != null && dateNow.isBefore(holder.getStartDate())){
        iter.remove();
    } else if(holder.getEndDate() != null && dateNow.isAfter(holder.getEndDate())){
        iter.remove();
    } else if (!checkStatus(holder)) {
        iter.remove();
    }

Answer 2

You have one IF and one IF-ElSE in your code, is that intended or you missed "else" there? Without this "else" you are likely to call iter.remove() more that once in an iteration.

        **if(dateNow.isAfter(holder.getEndDate())){
            iter.remove();
        **

Answer 3

I am not sure about your task, does this code resolve your problem?

contacts.stream().filter(x -> {
            if (dateNow.isBefore(holder.getStartDate()) || dateNow.isAfter(holder.getEndDate()) ){
                return false;
            }
            boolean status = chackStatus(x);
            if (!status){
                return false;
            }
            return true;
        }).collect(Collectors.toList());