How to loop through and delete elements in List and Set collections in java

When I was working on a project today, I needed to delete certain elements in List and Set. At that time, I used the method of traversing and deleting while traversing, but the following exception was reported:

ConcurrentModificationException

For Don’t forget it in the future, use a bad pen to record it as follows:

How to write the error code, that is, how to report the above exception:

Set<CheckWork> set = this.getUserDao().getAll(qf).get(0).getActionCheckWorks();
for(CheckWork checkWork : set){
  if(checkWork.getState()==1){
    set.remove(checkWork);
  }
}

Note: Using the above writing method will report the above ConcurrenModificationException, the reason is that the collection cannot be deleted while traversing.

The correct way to write it is as follows:

1. Traverse and delete List

List<CheckWork> list = this.getUserDao().getAll();
Iterator<CheckWork> chk_it = list.iterator();
while(chk_it.hasNext()){
  CheckWork checkWork = chk_it.next();
  if(checkWork.getPlanState()==1){
    chk_it.remove();
  }
}

2. Traverse and delete Set

Set<CheckWork> set = this.getUserDao().getAll().get(0).getActionCheckWorks();
        Iterator<CheckWork> it = set.iterator();
        while(it.hasNext()){
            CheckWork checkWork = it.next();
            if(checkWork.getState()==1){
                it.remove();
            }
        }

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