modify list while iterating java 8

rev2023.7.7.43526. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. EDITED the code to produce the exception, please note the list content: The behavior you are trying to reproduce is highly timing-dependent. How can I use a map to modify existing elements in a stream? All rights reserved. From my understanding the ListIterator.add() adds an element before the current element in the list, not after it. Not the answer you're looking for? 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), java stream mutate data with terminal operation, Split a list into sublists based on a condition with Stream api, How to modify an element of the Stream based on the value in a HashMap, Add an element to the list if it doesn't find it with lambda. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. to detect bugs. Which may not be acceptable in most cases. Any suggestions to avoid concurrent modification issue in this JAVA for loop please? Simply replacing one element by another doesn't count as a structural modification. How does the theory of evolution make it less likely that the world is designed? Yep. Easy solution is to create a copy of the list and iterate through that. Thanks for contributing an answer to Stack Overflow! In Java, can you modify a List while iterating through it? Decrementing index. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. But your statement is the one I was looking for. The second option is to use string builders instead of strings, which are mutable string creators/placeholders. I don't think data-race matters here, am I right? So performance considerations listed in other posts still hold. Not the answer you're looking for? Asking for help, clarification, or responding to other answers. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. 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. This class is designed for observer lists, which are rarely modified and often traversed. The only down-side of this approach is that you need to switch your for-each to a while. Critical issues have been reported with the following SDK versions: com.google.android.gms:play-services-safetynet:17.0.0, Flutter Dart - get localized country name from country code, navigatorState is null when using pushNamed Navigation onGenerateRoutes of GetMaterialPage, Android Sdk manager not found- Flutter doctor error, Flutter Laravel Push Notification without using any third party like(firebase,onesignal..etc), How to change the color of ElevatedButton when entering text in TextField. Do we have any way to achieve same behavior using Java 8 streams ? As it was mentioned before - you can't modify original list, but you can stream, modify and collect items into new list. Java 8 stream doesn't allow to modify the pointer itself and hence if you declare just count as a variable and try to increment within the stream it will never work and throw a compiler exception in the first place. total useless. How to modify a Collection while iterating using for-each loop without ConcurrentModificationException? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Do I have the right to limit a background check? But its performance in all other scenarios is so terrible that it should be practically never used. Iterator Methods Iterator interface has a total of 4 methods but initially, it was introduced with 3 methods but java 8 has come up with a new method. Overview Java 8 introduced the Stream API that makes it easy to iterate over collections as streams of data. My boss claims this code is fine (and it does appear to work), but I still don't think it is correct. Typo in cover letter of the journal name where my manuscript is currently under review. A sci-fi prison break movie where multiple people die while trying to break out. To learn more, see our tips on writing great answers. How JVM stack, heap and threads are mapped to physical memory or operation system. Any performance difference between using Streams and forEach in this case? What are solutions if you want to modify users? It also allows to replace the current element via set () method. Modifying Objects within stream in Java8 while iterating You can make use of the removeIf to remove data from a list conditionally. This answer is deleting the item from the list which isn't the answer to the question. I don't understand why Java API would have code "mainly" for debugging. to traverse the list in either direction, modify @Rad, Your conclusion is logically sound given the assumption that the iterator's. docs.oracle.com/javase/7/docs/api/java/util/concurrent/, Why on earth are people paying for digital real estate? But what about changing the elements in a List? It is a bit faster as it moves no elements to be removed later. No stream at all: just for modifying certain property from object collection you could directly use forEach with a collection as follows, We can change the property via map without creating new objects. Java: adding elements to a collection during iteration. Returns the index of the element that would be returned by a Supposedly something like this (illegal code): But we all know that the above code is not allowed. Java Collections Framework. Return Value: This method returns an unmodifiable view of the specified collection. Adding, removing and printing from ArrayList with Iterator. One workaround is to iterate backward in the list, which does not skip anything. 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), Iteration over a list (ConcurrentModificationException), Deal with concurrent modification on List without having ConcurrentModificationException, Running into java.util.ConcurrentModificationException while iterating list, Java How to add to an array list while looping, Concurrent modification excpetion with iterator adding to arraylist, ConcurrentModificationException when iterate through List, Java modifying list concurrently at different places, ConcurrentModificationException while iterating through List, altough not modifying it. I know it's not really long, but is there a better way to do this? I was just trying to indicate that the list was changing during iteration. In Java, can you modify a List while iterating through it. The simplest fast solution is to create an empty list and add all elements not less than three. 15amp 120v adaptor plug for old 6-20 250v receptacle? Given that, this code should work to set the new element as the next in the iteration: This will work except when the list starts iteration empty, in which case there will be no previous element. Is there a distinction between the diminutive suffixes -l and -chen? how to modify a list while iterating (intermediate) anthony explains The . +1 If you use CopyOnWriteArrayList you can modify it while iterating over it. @emory Yap. On the other hand, if the remove() happens before the last call to next() (and if this is noticed on the other thread - the memory model comes into play here) then you'll get the exception. Find centralized, trusted content and collaborate around the technologies you use most. It would really help if you could make this question self-contained. - Mkyong.com Java - How to remove items from a List while iterating? ListIterator (Java Platform SE 8 ) I think you can use nums.removeAll(toRemove), @maaartinus True, but it does depend a little bit on how, It used to be a native call when Java was terribly slow. What I would like to know is to modify the elements containing in the Set. In order to do that, you would have to look at the implementation of the iterator for ArrayList. Find centralized, trusted content and collaborate around the technologies you use most. (Or not, it depends - but premature optimization is the root of all evil), Add elements to a List while iterating over it. (Ep. Can you work in physics research with a data science degree? Bonus: if you iterate backwards, you can remove elements while iterating. For instance, ["apple", "orange"] to ["iapple", "iorange"]. My problem is that I want to expand a list with new elements while iterating over it and I want the iterator to continue with the elements that I just added. Would a different way of doing it, maybe using the set(E e) method of a ListIterator, be better? When are complicated trig functions used? I understand I wasn't using the iteration variable. How does Java HashMap store entries internally, Java: Changing the properties of an iterable object while iterating over it, Using the iterator over the same set more than once in java. Why did the Apple III have more heating problems than the Altair? 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: At the end the whole list will have the letter "D" as its content. Thank you and ZouZou for your answers. The size of the List is not being changed, but the object at the index is changing, so technically the List is being modified. 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. If you wanna create new list, use Stream.map method: If you wanna modify current list, use Collection.forEach: You can use just forEach. 2. So if you get into the last iteration of the loop before the remove() call, then you won't get an exception - hasNext() will just return false. Java - How to remove items from a List while iterating? Book set in a near-future climate dystopia in which adults have been banished to deserts. So this approach isn't any better, but it's a different way to do it. 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. 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. The question is how to replace/update/swap an item in the list while iterating. Connect and share knowledge within a single location that is structured and easy to search. You can use ListLterator for modifying list during iterating,it provides more functionality than iterator. There are several ways to iterate over List in Java. 15amp 120v adaptor plug for old 6-20 250v receptacle? I do assume (not exactly what you said, anyway). For example, in Java to modify a collection when another thread is iterating over it. and if you want to remove it, do the following: Java 8's stream() interface provides a great way to update a list in place. Also see the documentation redistribution policy.
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