remove item from list while iterating java

This article introduces how to safely delete items during while iterating List. Here is a code sample to use the iterator in a for loop to remove the entry. Use MathJax to format equations. To learn more, see our tips on writing great answers. 1. Java, removing elements from an ArrayList, iterating through collection - removing other element, Remove sublists from list while iterating, Java - removing an element in list while iterating it with a for index loop. To learn more, see our tips on writing great answers. Find centralized, trusted content and collaborate around the technologies you use most. Do you need an "Any" type when implementing a statically typed programming language? In the above example, we have created the ArrayList of different strings. To learn more, see our tips on writing great answers. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 587), The Overflow #185: The hardest part of software is requirements, Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g. ChatGPT) is banned, Testing native, sponsored banner ads on Stack Overflow (starting July 6), How to create a function to retains only the elements in the list that are contained in the specified list without using any third 3rd party. It is not recommended adding or removing elements from a list within a loop as an index of its elements, and the length of the list is changed. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Making statements based on opinion; back them up with references or personal experience. How to remove an element from ArrayList in Java? - GeeksforGeeks By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. (Ep. With Java 8, the most effective way to do this is use the removeIf(predicate) method on the list. Morse theory on outer space via the lengths of finitely many conjugacy classes. It's just that its often a, Last edit is exactly right. the key set can be a copy). Why add an increment/decrement operator when compound assignments exist? Normally when you remove an element from a collection while looping over the collection, you'll get a Concurrent Modification Exception. You can't and shouldn't modify a list while iterating over it. Extract data which is inside square brackets and seperated by comma, Extending the Delta-Wye/-Y Transformation to higher polygons. Is religious confession legally privileged? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Find centralized, trusted content and collaborate around the technologies you use most. (, How to sort an ArrayList in descending order in Java? So, if the code is multi-threaded use extra caution, or use concurrent collections. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. In this article, we will learn how the Iterators remove() method and the Collections remove() method works differently. To remove an element from the Collection, we can use the remove() method by taking the collection as a reference. Why do complex numbers lend themselves to rotation? Connect and share knowledge within a single location that is structured and easy to search. Looks good, but I'd replace the last loop in your second example with set.removeAll(removalSet). Yep your second answer will work, other than possibly running into memory problems +1 though. There are many ways in which you can do that. 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While iterating the List using For Loop, if an item is deleted, an exception may occur or a problem may occur in which it is not possible to search for an item. 587), The Overflow #185: The hardest part of software is requirements, Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g. Avoid angular points while scaling radius. Because I need to be able to remove arbitrary elements from the set at any point during the iteration over the set. Find centralized, trusted content and collaborate around the technologies you use most. But u can use removeAll(Collection c) api. You could try the java.util.concurrent.CopyOnWriteArraySet which gives you an iterator that is a snapshot of the set at the time of the iterator creation. Asymptotic behaviour of an integral with power and exponential functions. This answer is good for code before Java 8, but elron's answer is preferable if you are using Java 8. In the above output, users can see that once we remove the cat from the 2nd index, all elements in ArrayList shift by one index. How to modify population within for-loop? ConcurrentModificationException It will throw ConcurrentModificationException if these methods called during the iteration. Wait a moment and try again. You can use java.util.concurrent.ConcurrentHashMap. In what circumstances should I use the Geometry to Instance node? Removing While Iterating Sometimes we want to remove an element from an ArrayList while we're looping it. @ScalaNooB Just try, perhaps condition is not that simple to remove only 3-rd element. When remove(idx) gets called, the element at idx index gets deleted and all the next elements gets shifted to left. In fact, this solution is not even appropriate in the given situation (refactoring is appropriate, as suggested by others). FindBugs even has a detector for this: If you can use a for-each it's definitely the more elegant solution. What is this.tokens? Implementing hashCode and equals can have other unforeseen consequences. Then write the loop with an explicit iterator, do the stop and then iterator.remove(). In Java, Collection is an interface that contains different data types such as ArrayList, Set, etc. You can remove student from the list by using . Powered by, java.util.ConcurrentModificationException, * Java Program to remove an element while iterating over, // printing ArrayList before removing any element, // removing element using ArrayList's remove method during iteration, // This will throw ConcurrentModification, // printing ArrayList after removing an element, Exception in thread "main" [personal loan, home loan, auto loan, credit line loan, mortgage loan, gold loan], at java.util.ArrayList$Itr.next(ArrayList.java:831), Exception in thread "main" java.util.ConcurrentModificationException, * Java Program to remove an element while iterating over ArrayList, [personal loan, home loan, auto loan, credit line loan, mortgage loan, gold loan], [home loan, auto loan, credit line loan, mortgage loan, gold loan], best data structure and algorithms courses, Java 8 Stream filter() + findFirst Example Tutorial. 2. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Best Practices for Python Dependency Management for Python Application. In what circumstances should I use the Geometry to Instance node? Removing Element using Single Iterator List<ServerObject> copyList = new ArrayList<ServerObject>(this.servers); and use that as the list for the foreach-loop. Iterators were introduced mainly because enumerators couldn't handle deleting while enumerating. ChatGPT) is banned, Testing native, sponsored banner ads on Stack Overflow (starting July 6). How does the theory of evolution make it less likely that the world is designed? In my specific case it would take up a lot of memory and processing time to determine what to remove while iterating. It Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call). Remove elements from a list while iterating over it in Java We have taken the below pseudo code of the iterators remove() method from the official docs of Java. Browse other questions tagged, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site. Sorry I should make that clear, and will. I'd never heard of Collections.singleton() and I had no idea you could remove elements from a map by calling removeAll() on values()! (i.e remove (int index) and remove (Object element)) to remove elements from an ArrayList. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. java - Remove elements from collection while iterating - Stack Overflow Is there any potential negative effect of adding something to the PATH variable that is not yet installed on the system? java - Removing elements on a List while iterating through it - Code The error message is the following: The code doesn't compile. Is religious confession legally privileged? In what circumstances should I use the Geometry to Instance node? (, 10 Free Spring Boot Courses for Java developers (, Difference between ArrayList and HashSet in Java? That is why it is not advised to remove items while iterating, Because index of items gets changed after each removal. Your answer is the preferred one. Java 8 Collection#removeIf 2.1 removeIf examples 2.2 removeIf uses Iterator 3. How can I do this? @dzeikei as stated in the question, map.remove(key) threw a ConcurrentModificationException when he was looping over the map.keySet(). Required fields are marked *. I agree on the condition. If this method and the other method that modify the map are in synchronized blocks, I don't see why you have to do anything? When to use LinkedList over ArrayList in Java? 1. Create a method named removeItems () that accepts a list of names and inside it add a for-each loop that iterates through the list of names to find a name, and if it is found, we use the remove () method to remove it from the list. Would it be possible for a civilization to create machines before wheels? by calling removeAll()) won't be visible in the iterator, but are visible if you look at the set itself (and removeAll() won't throw). Avoiding the ConcurrentModificationException in Java | Baeldung For more details, look at Iterator.remove(). What would stop a large spaceship from looking like a flying brick? How to get Romex between two garage doors, Ok, I searched, what's this part on the inner part of the wing on a Cessna 152 - opposite of the thermometer. java - Removing items from a list - Stack Overflow By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How do I read / convert an InputStream into a String in Java? Let's look at the alternatives: Iterating over a copy, removing from original This is a simple solution for the underlying problem of your first code: A ConcurrentModificationException is thrown because you iterate through the list and removing from it at the same time. But the iterator will be useful when you are looping through the list and based on some condition you would like to remove an element from the list being inside the loop. Find centralized, trusted content and collaborate around the technologies you use most. Except possibly one: you could use a Collections.newSetFromMap(new ConcurrentHashMap(sizing params)). ArrayList remove () method Example Now, let's see an example of removing elements from ArrayList while looping using for () loop and ArrayList.remove () method, which is wrong, and the program will throw ConcurrentModificationExcetpion upon execution. Its not very obvious though that removing from the key set removes things from the map (i.e. It only removes the current element returned by the iterator, I need to remove multiple elements at a time. Removing element from ArrayList through Iterator, Removing items from list by index while looping through list, Removing an element from ArrayList while looping over it, Java removing an iterator that removes another element in the same list. You might find this article about ConcurrentModificationException has some advice in this area. zz'" should open the file '/foo' at line 123 with the cursor centered, Poisson regression with small denominators/counts. Do I have the right to limit a background check. Edit: Also if you are using a constant value in loop break condition like in above example i<10; you might get ArrayIndexOutOfBounds exception. Can you work in physics research with a data science degree? Do I have the right to limit a background check? Can Visa, Mastercard credit/debit cards be used to receive online payments? Using an Iterator Directly A for-each loop uses an Iterator behind the scenes but is less verbose. Making statements based on opinion; back them up with references or personal experience. Do I have the right to limit a background check? Why add an increment/decrement operator when compound assignments exist? [I How to Remove an Element from Array in Java with E How to remove duplicates from Collections or Strea How to Reverse String in Java with or without Stri What is double colon (::) operator in Java 8 - Exa How to copy Array in Java? change the code like this and it should workwhile (iterator.hasNext()){var student = iterator.next();if ( student.age == 21){iterator.remove();}. Connect and share knowledge within a single location that is structured and easy to search. (, 10 Courses to learn Java Programming for beginners (, How to create and initialize ArrayList in the same line? i think map.remove will thow concurrentModificationExceptiom, iterating over and removing from a map [duplicate], Iterating through a Collection, avoiding ConcurrentModificationException when removing objects in a loop, Why on earth are people paying for digital real estate? Is a dropper post a good solution for sharing a bike between two riders? Lets see the working experience to get a better understanding. Feel free to comment, ask questions if you have any doubt. Stuff that was removed from set in the meantime will be ignored. (, When to use ArrayList over LinkedList in Java? (Ep. Remove elements from a list while iterating over it in Java This post will discuss how to remove elements from a mutable list in Java that satisfies the given condition within a loop or iterator. ConcurrentModificationException in java while deleting entries from nested hashmap, HashMap's Iterator to prevent concurrent modification. Why do complex numbers lend themselves to rotation? What is the significance of Headband of Intellect et al setting the stat to 19? Connect and share knowledge within a single location that is structured and easy to search. How can I make this for loop repeatedly go through a list of arrays until a condition is reached? So, suppose you have a list containing 2, 3, 3, 4, 5. Example 3 ways to ignore null fields while converting Java 5 Differences between an array and linked list in What is difference between final vs finally and fi How to convert ArrayList to HashMap and LinkedHash How to code Binary Search Algorithm using Recursio Post Order Binary Tree Traversal in Java Without R 7 Examples to Sort One and Two Dimensional String How to prepare Oracle Certified Master Java EE Ent How to Check is given String is a Palindrome in Ja Top 5 Free Apache Maven eBooks for Java Developers. Can't enable error messages for PHP on my web server. Java : How to Remove Elements from HashMap while Iterating the canonical method of dealing with a changing array length is to start from the end of the array and work backwards. @LouisWasserman It's a trick question. How to perfect forward variadic template args with default argument std::source_location? Table of contents 1. java.util.ConcurrentModificationException 2. 2. If you use Iterator.remove(), then you are still safe. Let's see how we can get rid of an element in a loop: Share Not the answer you're looking for? But then it might be possible that an other thread appends a Server to the servers list while I am iterating over copyList but closeCurrentlyOpen is supposed to result in an emtpy list. The call to it.remove(); will remove the current item from p.eggMoves. . algorithm - Java: How to remove elements from a list while iterating Remove elements while iterating over ArrayList in Java, [JPA] Manually converting a native query result set to a list of DTOs, Create the target and copy a file via a single command, Debug Java web app hosted on Apache Tomcat. What are the advantages and disadvantages of the callee versus caller clearing the stack after a call? Asking for help, clarification, or responding to other answers. I'm running an iterator over an arraylist and am trying to remove an item when a condition is true. Also, I thought I would post my solution because there seems to be a need and I wanted to contribute the the excellent resource that is Stack Overflow. How do I avoid checking for nulls in Java? The neuroscientist says "Baby approved!" The list will be empty To subscribe to this RSS feed, copy and paste this URL into your RSS reader. However, to make each part of your code as safe as possible, I would recommend to use the Iterator approach. To learn more, see our tips on writing great answers. I then iterate over that collection and remove those indexes/objects from the original collection. Instead, your method starts over from the zeroth element every time a match is found, thereby repeatedly going over and over the same elements. If anyone knows how to add a lock onto this, I'd love to see how. The latter two examples assume school is a List. Java ArrayList.listIterator() with Examples - HowToDoInJava Is religious confession legally privileged? The later should close all servers and remove them from the server list. Maybe you can iterate over the map looking for the keys to remove and storing them in a separate collection. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Extending the Delta-Wye/-Y Transformation to higher polygons, Remove outermost curly brackets for table of variable dimension, Using regression where the ultimate goal is classification, Find the maximum and minimum of a function with three variables. In Java How to remove Elements while Iterating a List - Crunchify There is no need to call both it.remove(); and p.eggMoves.remove(selectedIndices[i]);. Are there nice walking/hiking trails around Shibu Onsen in November? Defining Our Collection First, we're going to illustrate two approaches that mutate the original data structure. 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