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

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 exception. The reason is that the collection cannot be traversed and deleted at the same time.

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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