在Java中同步使用for方法？

Question

I need to know about the usage of Synchronized using for methods in java .Please see the below code once.

Code :

public void upDateAllUsersStatus(UserDetails userDetails)
{


    for(Player p : userDetails.getPlayersList())
    {
        if(p != null)
        {
            String userId = p.getUserId();
            upDateUserStatus(userId );
        }
    }
}

public synchronized void upDateUserStatus(String name)
{           
    //here update status of user in db.
}

The above code used synchronized for method.is there any possibility of getting java.util.ConcurrentModificationException using synchronized above upDateUserStatus()?

Can you please suggest me what is the use of synchronized using for above method?.

Thanks in Advance.

Answer 1

If upDateUserStatus modifies the list of players stored in its userDetails object, the next iteration of the loop in upDateAllUsersStatus may throw a ConcurrentModificationException because the player list was modified (by upDateUserStatus ) while it's being iterated (by upDateAllUsersStatus ). The synchronized keyword doesn't help: that protects against concurrent execution in different threads, but it doesn't prevent an individual thread from modifying a list while that same thread is iterating it.

Your code looks strange, though, and I suspect it has other problems: you're iterating the list of players stored in userDetails , but you don't actually do anything with the individual Player objects. You just call upDateUserStatus multiple times on the same userDetails object. Did you intend for upDateUserStatus to take a Player argument instead of a UserDetails ? If so, that should be safe, since an individual Player (presumably) can't modify the list of other players.