I was just trying to indicate that the list was changing during iteration. Let's look at the alternatives: 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. How I can add objects into an ArrayList when I'm using this ArrayList in a for loop? We can do that by using hasNext (), next (), previous () and hasPrevious () methods. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Returns the next element in the list and advances the cursor position. What could cause the Nikon D7500 display to look like a cartoon/colour blocking? I like it! EDIT: My original code would have thrown a ConcurrentModificationException. But your statement is the one I was looking for. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Can anyone explain why it behaves like this? My boss claims this code is fine (and it does appear to work), but I still don't think it is correct. Some Iterator implementations (including those of all the general purpose collection implementations provided by the JRE) may choose to throw ConcurrentModificationException if this behavior is detected. Asking for help, clarification, or responding to other answers. API Note: This method exists mainly to support debugging, where you want to see the elements as they flow past a certain point in a pipeline: reference: I don't understand why this operation is "mainly" for debugging. How does the theory of evolution make it less likely that the world is designed? Can we remove any element by using for each loop? Now, it's a JVM intrinsic, which means that the JITc replaces the code by something smart and fast (using XMM registers). There are 3 problems in your approach to solve the problem. 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. This is the approach I would recommend in most cases. ListIterator (Java Platform SE 8 ) java.util Interface ListIterator<E> All Superinterfaces: Iterator <E> public interface ListIterator<E> extends Iterator <E> An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator's current position in the list. Concurrent stream sources are those whose Spliterator reports the CONCURRENT characteristic. So this approach isn't any better, but it's a different way to do it. rev2023.7.7.43526. The notable exception to this are streams whose sources are concurrent collections, which are specifically designed to handle concurrent modification. We might think that it's always faster to divide the work on more cores. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This answer is deleting the item from the list which isn't the answer to the question. Different maturities but same tenor to obtain the yield, Some of them printed and an exception is thrown. Connect and share knowledge within a single location that is structured and easy to search. would be wrong to write a program that depended on this exception for Are there ethnically non-Chinese members of the CCP right now?
Remove elements from a list while iterating over it in Java +1 If you use CopyOnWriteArrayList you can modify it while iterating over it. On the up-side, this is among the fastest for bigger lists. Can we use work equation to derive Ohm's law? What is the reasoning behind the USA criticizing countries and then paying them diplomatic visits? As the API documentation for peek shows, it is there to show intermediate level results for debugging. I have productListArray and I would like to add product into it but each product has unique ID and unique name and I am getting some errors, Space Invaders generate initial Asteroids Java Failure, arrayList only updates 2 elements when using forEach, Adding object to arraylist unless it's already there. A. I don't think data-race matters here, am I right? To do structural modification on the source of the stream, as Pshemo mentioned in his answer, one solution is to create a new instance of a Collection like ArrayList with the items inside your primary list; iterate over the new list, and do the operations on the primary list. This not only solves the problem unambiguously, but avoids the gotchas of not knowing how an iterator is going to act. @Rad, Your conclusion is logically sound given the assumption that the iterator's. Learn more about Stack Overflow the company, and our products. this does not work when adding to a list (if 'c' is a List<>) I get java.util.ConcurrentModificationException. What are solutions if you want to modify users? I think his question is more of "why do I sometimes get lucky" rather than "why did the Exception occur at all? Is there a distinction between the diminutive suffixes -l and -chen? So performance considerations listed in other posts still hold. Would it be possible for a civilization to create machines before wheels? 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. rev2023.7.7.43526. You can make use of the removeIf to remove data from a list conditionally. There are similar questions on SO talking about remove or add element while iterating a Java Set. Modifying an Array list while I am iterating over it, In need of iterating and modifying arraylist (or similar) at the same time. Find centralized, trusted content and collaborate around the technologies you use most. Is it possible to achieve this in some other way? Yes, you can modify or update the values of objects in the list in your case likewise: However, the above statement will make updates on the source objects. Below method increase the age by 2. References, when reassigned, don't change the actual object it refers to.
Streams will make it in only one loop. Thanks for contributing an answer to Stack Overflow! You can't modify a Collection while iterating over it using an Iterator, except for Iterator.remove (). Possible Duplicate: From my understanding the ListIterator.add() adds an element before the current element in the list, not after it. Sci-Fi Science: Ramifications of Photon-to-Axion Conversion, Commercial operation certificate requirement outside air transportation. But agreed, it's still, Iterating using an old-fashioned for-loop does solve the, Removing elements on a List while iterating through it, Why on earth are people paying for digital real estate? @Sergii Lagutin Can we update multiple fields, ex name as well as the country in a single for each loop? From non-interference section of stream package documentation we can read that: when you construct a string, say new String("hello"), you can't further modify it's inner value. Is there a distinction between the diminutive suffices -l and -chen?
How to Remove Objects From ArrayList while Iterating in Java - Example Languages which give you access to the AST to modify during compilation? 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. rev2023.7.7.43526. Are there ethnically non-Chinese members of the CCP right now? When to use LinkedList over ArrayList in Java? My boss claims this code is fine (and it does appear to work), but I still don't think it is correct. If I got it correctly, the output should be either three items printed or some of them printed and an exception, no matter what. Which returns an updated list back, without hampering the old one. Would a different way of doing it, maybe using the set(E e) method of a ListIterator, be better? My impression is that Java is not particularly suitable for FP. If he had posted it as a comment, someone most likely would have told him he shouldn't post answers as comments. I see it in ArrayList. Not the answer you're looking for? Java 8 provides a safer method to conditionally remove items from stream using a filter Remove elements from collection using Java 8 Lambda expression List<String> names = new ArrayList (asList ( "munish", "ravneesh", "rajneesh" )); names.removeIf (name -> "munish" .equalsIgnoreCase (name)); System.out.println ( "names = " + names); We'll cover a few examples using a while loop, Java 8, and a few common libraries. You can't modify a Collection while iterating over it using an Iterator, except for Iterator.remove(). Is there any potential negative effect of adding something to the PATH variable that is not yet installed on the system? There are 3 problems in your approach to solve the problem.
3rd - Strings are immutable. 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). When are complicated trig functions used? You could do it with map but that would mean you have some intention changing something on the list, where you actually you dont. How do I efficiently iterate over each entry in a Java Map? Science fiction short story, possibly titled "Hop for Pop," about life ending at age 30. Instead of modifying the collection I would suggest using, That is actually correct, but: this depends on the specific class that is used here. All rights reserved. 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? Thanks for contributing an answer to Stack Overflow! To get rid from ConcurrentModificationException Use CopyOnWriteArrayList. Characters with only one possible next character. I understand I wasn't using the iteration variable. You would need to create a new Set with the new values. Code Review Stack Exchange is a question and answer site for peer programmer code reviews. 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. Any suggestions to avoid concurrent modification issue in this JAVA for loop please? The element is inserted immediately before the element that What is the verb expressing the action of moving some farm animals in a field to let them eat grass or plants? How does the theory of evolution make it less likely that the world is designed? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA.
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