can we remove element from list while iterating java

Why do I get an UnsupportedOperationException when trying to remove an element from a List? Here are the exact steps to remove elements from HashMap while Iterating 1. Java - List If any elements are removed, the method returns true, and if the provided filter is null, it throws a NullPointerException. The first approach will work, but has the obvious overhead of copying the list. This method removes all the elements that evaluate the Predicate to true, and any runtime exceptions that occur during the iteration are passed to the caller. Easy solution is to create a copy of the list and iterate through that. Are there ethnically non-Chinese members of the CCP right now? The method returns true if the collection changes as a result of the call. The problem for me occurs when the above code can take place in another loop, which is actively iterating the original list. There are several ways to remove elements from the list while iterating some of them are: Using for in loop Using List Comprehension Using filter () function Method #1:Using for in loop To accomplish this, we must first make a copy of the list, and then iterate over that copied list. Similar to what Bombe suggested, but in less lines of code by iterating on the list copy, but removing from the original list; Personally I think this looks nicer than iterating with an iterator. Does "critical chance" have any reason to exist? Thanks for contributing an answer to Stack Overflow! What is the number of ways to spell French word chrysanthme ? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. This is a simple object with a single int field. I think it looks cleaner and won't throw this error. Method-2: collectionRemoveIfObjectEquals Method. We will use below 5 methods to remove an element from ArrayList while iterating it. If yes, then returns True otherwise False. Can I still have hopes for an offer as a software developer. How to Speed up WordPress Site by tuning WP Super Cache Settings? java - Removing item from list while iterating - Stack Overflow Second, not all List implementations offer direct access to the elements (as ArrayList does). Here a loop with remove instruction. Built on Genesis Our Partners: Kinsta & MailerLite. The first technique consists in collecting all the objects that we want to delete (e.g. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. You can modify collection during iteration using iterator.remove() only. Asking for help, clarification, or responding to other answers. Only second approach will work. I would say this is bug prone.. having 2 lists where we dont need the second. Add elements to a List while iterating over it. (Java) When are complicated trig functions used? So either we need to create a copy of the list for iteration and then delete elements from the original list, or we can use the list comprehension or filter() function to do the same. In Java, if we remove items from a List while iterating it, it will throw java.util.ConcurrentModificationException. It's just that we need to wait until after iterating before we remove the elements. How to fix Access-Control-Allow-Origin (CORS origin) Issue? How to Add Multiple Values for Single Key In HashMap in Java, [Fixed] java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.util.ArrayList, Core Java Tutorial with Examples for Beginners & Experienced. So we can use the filter() function to filter elements from a list while iterating over it. Please leave a comment to start the discussion. You cannot directly delete the element from the list while iterating because of doing you get Runtime Error because the iterator is now pointing to NULL and the address of the next element of the list gets lost and you cannot access the list anymore. We want to delete elements from the list while iterating over it, based on some conditions like all occurrences of 54 and 55. How can i counter a ConcurrentModificationException? It deleted all the occurrences of 54 and 55 from the list while iterating over it. For simple removal of all "A" as you mention List.filter would be most simple and sufficient. x[:] = [i for i in x if foo]), because every time you call. How to format a JSON string as a table using jq? What is the number of ways to spell French word chrysanthme ? Can the Secret Service arrest someone who uses an illegal drug inside of the White House? Remove elements from a list while iterating over it in Java Avoiding the ConcurrentModificationException in Java Is religious confession legally privileged? document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); This site uses Akismet to reduce spam. If you are working with lists, another technique consists in using a ListIterator which has support for removal and addition of items during the iteration itself. In this tutorial, you have learned what is ConcurrentModificationException and how it comes about when removing items while traversing through a list. What is the Modified Apollo option for a potential LEO transport? But now you have started using conditional statements! 1. modify 2. delete an element from a list when iterating over it using the enhanced for loop, for example http://jmonkeyengine.com/mark/?p=147. for edge in node.edgeList: . 3. The problem is that when you remove an item, the following items are all shifted back by one, but the location of the index remains the same. Removing elements is a necessary task for any container. What is the reasoning behind the USA criticizing countries and then paying them diplomatic visits? Stay up to date & never miss an update! haha! You need to use the iterator directly, and remove the item via that iterator. How to Flatten, Unflatten Complex JSON objects into Map-Like Structure, How to Find Duplicate Elements from List? @Mr_Skid_Marks could you add an example so we can produce your issue? The right way to remove objects from ArrayList while iterating over it is by using the Iterator's remove () method. Is there any potential negative effect of adding something to the PATH variable that is not yet installed on the system? But I never came across a suitable example illustrating the 'modify' operation on the list. Just curious, why do you create a copy of foolist rather than just looping through foolist in the first example? Thank you for your valuable feedback! Is there any potential negative effect of adding something to the PATH variable that is not yet installed on the system? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. I agree. Operating on and Removing an Item from Stream Fix Higher CPU, Memory Usage for WordPress site, Export WordPress Post Title, Post URL & Featured Image in CSV. Making statements based on opinion; back them up with references or personal experience. Note: prefer 'for' over 'while' also with iterators to limit the scope of the variable: for(Iterator itr = fooList.iterator(); itr.hasNext();){}. HashMap Vs. ConcurrentHashMap Vs. SynchronizedMap Tutorial, IntelliJ IDEA Project/Module and latest Java setup (Java 17 or newer). In Java How to remove Elements while Iterating a List - Crunchify I have a graph implementation. The stream() method will be followed by a call to the filter() method that accepts a Predicate which is a functional interface that accepts a single input and returns a boolean. I have tried the remove() method inside of my conditional if statement but doesn't work. We want to delete elements from the list while iterating over it, based on some conditions like all occurrences of 54 and 55. How to remove element from a list while iterating? Do I remove the screw keeper on a self-grounding outlet? Exception in thread main java.util.ConcurrentModificationException, Customer{firstName=john, lastName=doe}, How to remove element from Arraylist in java while iterating. Below is the implementation of the above topic. (Ep. It is safe to call while iterating. In addition to using the Iterator directly (which I would recommend) you can also store elements that you want to remove in a different list. Java 8 Collection#removeIf 2.1 removeIf examples 2.2 removeIf uses Iterator 3. How to remove an item at a given index from Array/List in Elm? 1 1 New contributor Add a comment 1 Answer Sorted by: 0 You can't modify a collection while you're streaming over it. Therefore, if you remove element 0, then the element 1 becomes the new element 0. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Get quality tutorials to your inbox. Remove the item from the list if it is found and log the modified list to the console to verify that the item was removed. First, every time you remove an element, the indexes are reorganized. Top 5 ways to Download a File from any given URL in Java, How to Convert Map / HashMap to JSONObject? Second, if you're using concurrency, use the CopyOnWriteArrayList and remove the item with, to provide a good example for the scenario, check this. I don't know if lists et al have. Java get element from List while the size is changing. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Are there any reasons to prefer one approach over the other (e.g. Find centralized, trusted content and collaborate around the technologies you use most. Then we can assign the new list to the same reference variable, which was part to the original list. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. What could cause the Nikon D7500 display to look like a cartoon/colour blocking? In Java, it's straightforward to remove a specific value from a List using List.remove (). Let me know if you face any problem running this Java program. When we deleted 52, it internally shifted the indexing of all the elements after 52, and our iterator becomes invalid. ArrayList.Iterator removes the element from the collection and shifts subsequent data to the left whereas, LinkedList.Iterator simply adjusts the pointer to the next element. We'll also check the more robust ListIterator extension which adds some interesting functionality. Will just the increase in height of water column increase pressure or does mass play any role in it? However, efficiently removing all occurrences of a value is much harder. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. java - Removing an element in a list while iterating through it while How to Remove an Element from Collection using Iterator Object in Java? Then we assigned the new list to the same reference variable. Getting a ConcurrentModificationException thrown when removing an element from a java.util.List during list iteration? Java Properties File: How to Read config.properties Values in Java? How to wake up a std::thread while it is sleeping? Do I remove the screw keeper on a self-grounding outlet? Depending on what you're doing, a list comprehension is preferable. If the list is sorted, and you want to remove consecutive elements you can create a sublist and then clear it: Since the sublist is backed by the original list this would be an efficient way of removing this subcollection of elements. listIterator.add (Element e) - The element is inserted immediately before the element that would be returned by next () or after the element that would be returned previous () method. Step-by-Step Guided Tour, Top 3 Free and Best WordPress Tracking Plugins and Services, Better Optimize WordPress Database - All in One Guide. for i in l[:]: @kindall, @GoingTharn, both good points. Never considered this as I typically just used it to remove a single item I was looking for. Perform maven-clean-install, Create a Simple In Memory Cache in Java (Best Lightweight Java Cache). Log the modified list to the console and observe that the customer with the given name was removed from the list. Is speaking the country's language fluently regarded favorably when applying for a Schengen visa? 1: ConcurrentModificationException 2: , 1: List Index Index 2: , 3: Collection.removeIf () 4: Iterator Be the first to rate this post. For those working with Java 8 or superior versions, there are a couple of other techniques you could use to take advantage of it. 1. How to Create WordPress Custom Post Type (CPT) and Taxonomy? Why removing element from list using iterator causes ConcurrentModificationException? So it gave an effect that we have removed elements from the list while iterating over it. Create class: CrunchifyRemoveItemFromList.java. The first attempt iterates on a copy, meaning he can modify the original. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Ways to Iterate Over a List in Java Consenting to these technologies will allow us and our partners to process personal data such as browsing behavior or unique IDs on this site and show (non-) personalized ads. This would be my preferred method for iterators that support remove(). If you want to "add" this approach would also work, but I would assume you would iterate over a different collection to determine what elements you want to add to a second collection and then issue an addAll method at the end. Now there is this one function that is supposed to delete some edges that the node has attached. What does "Splitting the throttles" mean? So if we are iterating over a list and we deleted an element from it while iterating over it, it will cause iterator invalidation and give unexpected results. Love SEO, SaaS, #webperf, WordPress, Java. These are discussed below: We have seen that moving forward in the list using a for-loop and removing elements from it might cause us to skip a few elements. For example, If we try to remove an item directly from a List while iterating through the List items, a ConcurrentModificationException is thrown. Both collections would keep references to the same objects. Removing an element of a Collection inside a thread inside the iterator, Remove item from list while using iterator without acess to iterator Java, Arraylist iterator concurrent modification exception when removing item, Removing items from a list while iterating over it, How can i remove an object from the ArrayList while iterating without getting an "Concurrent Modification Error". java - Removing elements on a List while iterating through it - Code Your choices will be applied to this site only. Add Google reCAPTCHA to WordPress Comment form, Display Title on Previous Post and Next Post mouse hover link, Remove the nofollow attribute from WordPress comments for self-links. What does that mean? There is no such change in the while and for loop, just the way to increment is changed which can be quite confusing. Instead of removing elements as moving forward in the list, we create a collection of such elements and delete them later. About DCMA Disclaimer and Privacy Policy. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. private void removeMethod (Object remObj) { Iterator<?> it = list.iterator (); while (it.hasNext ()) { Object curObj= it.next (); if (curObj == remObj) { it.remove (); break; } } } It throws NoSuchElementException if no more element is present. For example. If you are going to to this, at least do it backwards to avoid this problem. You get the exception in the example that you post, because the list over which your iterator iterates, has changed, which means that the iterator becomes invalid. How can I remove a mystery pipe in basement wall and floor? What is the significance of Headband of Intellect et al setting the stat to 19? So you save memory and time. Find centralized, trusted content and collaborate around the technologies you use most. While notifying the listeners of an event, other listeners may no longer be needed. | Search by Value or Condition, Python : Check if all elements in a List are same or matches a condition, Python : Check if a list contains all the elements of another list, Python : How to add an element in list ? Method-3: collectionteratorRemove Method. The Java 8 Stream will allow us to perform aggregate operations on the stream to get our desired output. 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