Java for loop remove from list3/2/2024 ![]() an element that matches certain conditions using ArrayList's remove method.įor example, in the below code we have first added a couple of good programming books like Programming Pearls, Clean Code, Effective Java, and Code Complete into ArrayList and then removing any element which has Code in its title. In this program, we are iterating over ArrayList using the enhanced foreach loop and removing selective elements e.g. This is the first example of reproducing the concurrent modification exception in Java. ![]() ArrayList itself then you can also join these Java Collections and Stream API Courses to learn this important API in depth.ĬoncurrentModificationException in Single Thread In this article, I'll explain this error and we'll many code examples to reproduce this code even with a single thread and learn how we can avoid concurrent modification errors while modifying an ArrayList in Java.ītw, if you are not familiar with collection classes e.g. though it seems natural thinking that maybe some other thread is trying to modify the collection at the same time, it's usually breaking the Java rule. Or you can copy all the ones you want to keep into a new list as you iterate, and then discard the old list when done. It's misnomer, don't get fooled away by this. The Java 8 way to remove it from the List without Iterator is: li.removeIf() i.e.In fact, there is no clear semantics for it. Most of the time ConcurrentModificationException comes even without multiple threads modifying the list. The remove () method in the Collection interface is explicitly specified as an optional operation: remove (Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation). ![]() The main problem with this error is that it confuses developers that the list is getting modified by multiple threads and that's why Java is throwing this error, it's not true. CopyOnWriteArrayList, which operate on a copy of list rather than the original list. It's an unwritten rule in Java that while looping through the list, you should not add() or remove() elements until the collection supports fail-safe Iterator e.g. If you use classical for loop with the index or enhanced for loop and try to remove an element from the ArrayList using remove() method, you will get the ConcurrentModificationException but if you use Iterator's remove method or ListIterator's remove() method, then you won't get this error and be able to remove the element. Usage would be: list1.retainAll (list2) It might not be any more efficient than a naive iteration approach, however, unless you use Set. In other words, removes from this collection all of its elements that are not contained in the specified collection. One of the common problems while removing elements from an ArrayList in Java is the ConcurrentModificationException. Retains only the elements in this collection that are contained in the specified collection.
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