java add to list while iterating

You could also use an extra list to keep track of the new elements and add that to the original list after the processing is over: Inserts the specified element into the list (optional operation). The code above doesn't make an exception near String.valueof. No obviously, but I want to add while iterating because I need to process also new added elements during the iteration and this is could be the shortest way. How to Start Your First Self-Hosted WordPress Blog? Perform maven-clean-install, Create a Simple In Memory Cache in Java (Best Lightweight Java Cache). and you can use queue.removeFirst() to deal with item in the queue from top-to-down. java - Is it safe to add items to a linked list while iterating - Stack Signup for news, latest articles and special offers!! Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, Java Adding items to ArrayList while iterating it, Jamstack is evolving toward a composable web (Ep. Flutter change focus color and icon color but not works. EDIT : The AbstractList maintains a "modCount"(modification count) attribute which counts the number of add, remove etc that you made on the list. Why should we take a backup of Office 365? How do I store ready-to-eat salad better? It is available since Java 1.2. public Object next (); eg. 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. Why do oscilloscopes list max bandwidth separate from sample rate? docs.oracle.com/javase/7/docs/api/java/util/concurrent/. Making statements based on opinion; back them up with references or personal experience. erforms an action for each element of this stream. How to manage stress during a PhD, when your research project involves working with lab animals? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. java - null Object in Iterator - Stack Overflow +1 If you use CopyOnWriteArrayList you can modify it while iterating over it. Solution 1 There is nothing wrong with the idea of modifying an element inside a list while traversing it (don't modify the list itself, that's not recommended), but it can be better expressed like this: for ( int i = 0; i < letters.size (); i++) { letters. Use reflection to modify the accessibility of the Node class, which gives you references to the double links, so you don't need to start iteration over with get(index), which should not be used in performant code. To safely update items in the list, use map(): To safely remove items in place, use filter(): I understand that in Java a Collection should not be modified while iterating through it, such as removing or adding elements. what is this theme. Is Benders decomposition and the L-shaped method the same algorithm? Why does Isildur claim to have defeated Sauron when Gil-galad and Elendil did it? Thanks. Knowing the sum, can I solve a finite exponential series for r? iterating? For loop uses a variable to iterate through the list. ), so if you have more than one elements in the list, it will not add the new ones to the end, but between the current one and the one returned by next(). Fundamentally, you're modifying a list in one thread while iterating over it in another, and the list implementation you're using does not support that. Thanks for contributing an answer to Stack Overflow! 589), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g., ChatGPT) is banned. I want to iterate over list and increment orders by one. File.copy() or File.move() - How to fix file.FileAlreadyExistsException? Q&A for work. Why does awk -F work for most letters, but not for the letter "t"? Can you solve two unknowns with one equation? Step-by-Step Guided Tour, Top 3 Free and Best WordPress Tracking Plugins and Services, Better Optimize WordPress Database - All in One Guide. System.out.println(temp); What is the "salvation ready to be revealed in the last time"? Comment Policy: We welcome relevant and respectful comments. Let's begin with the approach traditionally used before Java 8. for(String temp:crunchifyList){ But this is probably the closest the OP is going to come to a (straight-forward) solution. This is the recommended approach to avoid concurrent modification exception. Making statements based on opinion; back them up with references or personal experience. The requirements to add while iterating and include the added items in the iteration can only be met if you don't use an iterator for iteration since there is no way to recompute the state of your iterator every time an element is added. In Java, a List is an interface of the Collection framework. If you indeed want to place the new elements at the end of the list, use queue.add(), In general, it is not advisable to modify a collection while traversing it via an iterator, so I suggest you use the second approach (collect the extra elements in a separate list and add them to the original at the end). For Loop: 0.015s Is tabbing the best/only accessibility solution on a data heavy map UI? Add an element at the end of a LinkedList. *; class GFG { public static void main (String [] args) { List<Integer> my_list = Arrays.asList (10, 20, 30, 40, 50); System.out.print ("Iterating over ArrayList: "); Why in TCP the first data packet is sent with "sequence number = initial sequence number + 1" instead of "sequence number = initial sequence number"? For example, what if we have. Create First WordPress Plugin? . We'll cover a few examples using a while loop, Java 8, and a few common libraries. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, Modify a list while it is being iterating, Jamstack is evolving toward a composable web (Ep. how to add an element at the begining of a linked list? This list iterator extends from the iterator interface. Peek method should only be used for debugging, Update element in the list while iterating Java8, Modify property value of the objects in list using java 8 streams, docs.oracle.com/javase/8/docs/api/java/util/stream/, Jamstack is evolving toward a composable web (Ep. While Loop: 0.01s List crunchifyList = new ArrayList(); All comments are manually moderated and those deemed to be spam or solely promotional will be deleted. A player falls asleep during the game and his friend wakes him -- illegal? , Index List , Exception . Connect and share knowledge within a single location that is structured and easy to search. The following code will throw a ConcurrentModificationException: LinkedList does not override iterator() and the default implementation, defined in AbstractSequentialList is to call listIterator(), and LinkedList does override listIterator. Stream ForEach: 0.361s. Keep going. IntelliJ IDEA - How to Set Latest Java SDK & version not supported. Is it safe to add items to a LinkedList while iterating? Find centralized, trusted content and collaborate around the technologies you use most. Java List add () This method is used to add elements to the list. Also as correctly pointed by "Vasanth Senthamarai Kannan " you don't need second list as you are not modifying structure of list, you can use replaceAll() just define a method like incrementOrder(). How to fix Access-Control-Allow-Origin (CORS origin) Issue? Hi Lee try saving each iteration value to array and if required in multidimensional array. The problem of my code is that isn't working and my first for loop cycles only one time (At first it dirs contains only the root directory). Your fix should be e.setOrders(e.orders += 1). The element is inserted immediately before the next element that would be returned by next, if any, and after the next element that would be returned by previous, if any. 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Improve The Performance Of Multiple Date Range Predicates, Replacing Light in Photosynthesis with Electric Energy. Hi, list.stream().forEach() is not necessary. 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. Thanks for contributing an answer to Stack Overflow! Assuming you don't have a hard requirement to use an iterator then you can just shelve it and 'iterate' over the list by index instead: If you cannot use another list, you could solve your problem by keeping a count of the number of elements you processed via the iterator and compare that to the original size of the list: all new element will be at the end of the list, so you can end your loop when you have reached the original size. Example: Writing a tex package for better auto brackets. ? Why do oscilloscopes list max bandwidth separate from sample rate? Is there a way to create fake halftone holes across the entire object that doesn't completely cuts? C Program to insert an array element using pointers. String.valueOf implemented like that. Adding elements to a collection during iteration. Would a different way of doing it, maybe using the set(E e) method of a ListIterator, be better? The ArrayList iterator implementation appears to only detect invalid modicifications on the call to next(), not on the call to hasNext(). }. Is it legal to cross an internal Schengen border without passport for a day visit. for(int i=0;i Advance For Loop Example..); Best way to Read JSON Object from any File in Java? I have List of Customer object. Solving ConcurrentModificationException while Iterating over ArrayList in Java What you want is to use explicitely a ListIterator, instead of an Iterator, and use ListIterator.add: The new element is inserted before the element that was returned by next() so subsequent calls to next() are unaffected. So if the for loop creates x, how do I save each iteration to x(i)? Are you looking for complete code? It's not a good idea to use an enhanced for loop in this case, you're not using the iteration variable for anything, and besides you can't modify the list's contents using the iteration variable. Let us first create an ArrayList . List<String> letters = new ArrayList<String> (); letters.add ("A"); letters.add ("B"); letters.add ("C"); int i = 0; for (String letter : letters) { letters.set (i, "D"); i++; } So, I'm not talking about modifying the object stored at an element; I'm talking about changing what the object is. I read a lot of answers on stackoverflow (in fact this is a one of them) but non of them seems to work (obviously I'm making some mistakes). 3 Answers Sorted by: 44 You can't modify a Collection while iterating over it using an Iterator, except for Iterator.remove (). My boss claims this code is fine (and it does appear to work), but I still don't think it is correct. Thanks for stopping by and sharing your thoughts . If you would like to change the data in the list, you would need to use a traditional for loop. Post-apocalyptic automotive fuel for a cold world? By using this website, you agree with our Cookies Policy. end = Instant.now(); What is more efficient: sorted stream or sorting a list? We help clients transform their great ideas into reality! If you change the list while iterating over it, it will throw ConcurrentModificationException. //System.out.println(temp); java - Update element in the list while iterating Java8 - Stack Overflow
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