I wrote the function removeAllElements, but it does not work if the size of the List is greater than 1. I am saying that iterators can be part of a correct solution, assuming that you use them the right way. Why do oscilloscopes list max bandwidth separate from sample rate? rev2023.7.13.43531. [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? Cat may have spent a week locked in a drawer - how concerned should I be? I guess this is the trivial scenario. Thanks for contributing an answer to Stack Overflow! In any example where only one thread can access the collection, using remove() is 100% safe, for all standard collection classes. What is the purpose of putting the last scene first? Remove two objects at the same time from an ArrayList without causing a ConcurrentModificationException? Vim yank from cursor position to end of nth line, I think my electrician compromised a loadbearing stud. Conclusions from title-drafting and question-content assistance experiments How can I make this for loop repeatedly go through a list of arrays until a condition is reached? How do I get the index of an iterator of an std::vector? The idea is that if you would forget to use break; or return; then you would have problems. How to Get Random Elements from Java HashSet? Implementing Iterable in Java remove() and iterator(). 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. For more details, look at Iterator.remove(). What you want to do by removing same item (that is at index i) again and again? If there's only one thread that iterates over and modifies the collection, there's no problem with using the iterator's remove method. Getting submap, headmap, and tailmap from Java TreeMap, Java Program to Convert a Decimal Number to Binary Number using Stacks. This is the only legal way to structurally modify a LinkedList during iteration. Whats wrong with it? Does a Wand of Secrets still point to a revealed secret or sprung trap? Is this possible? When did the psychological meaning of unpacking emerge? Example How to reverse bits of an integer in Java? Tikz Calendar - how to pass argument with '\def'. Negative literals, or unary negated positive literals? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Remove elements from collection while iterating Ask Question Asked 11 years, 2 months ago Modified 4 months ago Viewed 402k times 318 AFAIK, there are two approaches: Iterate over a copy of the collection Use the iterator of the actual collection For instance, Exception in thread main java.util.ConcurrentModificationException Improve The Performance Of Multiple Date Range Predicates. Can my US citizen child get into Japan, if passport expires in less than six months? In multi-threaded processing of data, it depends on how (synchronized/asynchronized processing, using a different list for collecting the elements to be removed etc.) So you need to do something like this: public void removeAllElements () { Iterator itr = this.elements.iterator (); while (itr.hasNext ()) { Object e = itr.next (); itr.remove (); } } If you want to just remove all the elements . It would compile and run without exceptions. What is the "salvation ready to be revealed in the last time"? Best article to use in complex-compound sentence. How to delete last x element of a list after performing some operation on them? How to Remove Objects from Collection or List in Java? Iterator remove If a thread modifies a collection directly while it is iterating over the collection with a fail-fast iterator, the iterator will throw this ConcurrentModificationException. Is Java "pass-by-reference" or "pass-by-value"? When it comes to multithreaded environment, it really depends on how do you organize the code. The removeIf() method removes all elements from the collection which satisfy the provided predicate. Implementing hashCode and equals can have other unforeseen consequences. Any thoughts on this? The reason for this output is depicted below: Iterator.remove will work as long as no other thread changes the Collection while you're iterating over it. By using Iterator, we can perform both read and remove operations. When did the psychological meaning of unpacking emerge? I am assuming that tokens is your Arraylist? Can Loss by Checkmate be Avoided by Invoking the 50-Move Rule Immediately After the 100th Half-Move? Why is type reinterpretation considered highly problematic in many programming languages? Read our. Which superhero wears red, white, and blue, and works as a furniture mover? To learn more, see our tips on writing great answers. This will not have a big impact on performance thanks to the fact that you are using a Set. (, How to synchronize an ArrayList in Java? Iterators differ from enumerations in two ways: Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics. Add the number of occurrences to the list elements. For guitar sight reading, how do you not confuse between 3rd and 4th string? Iterator.remove (Showing top 20 results out of 70,506) If so, can anyone give an example where using the .remove() method of an iterator is useful outside of testing? How do I generate random integers within a specific range in Java? Here is an interesting piece of code (could be a good interview question). The following code demonstrates this: For Java 8 and above, you can use the removeIf() method with lambda expressions. Of course in Java 8+ you can achieve almost the same with Streams: However, this method creates a new collection, rather than modifying the existing one (like in the case with iterators). This program demonstrates that if you use the Collections remove method while traversing over Collection using Iterator to remove the current element then you can get ConcurrentModificationException and by using Iterator's remove method you can easily avoid it. Why is Singapore placed so low in the democracy index? How do I store ready-to-eat salad better? A Guide to Iterator in Java | Baeldung Removing Items from a Collection Iterators are designed to easily change the collections that they loop through. Conclusions from title-drafting and question-content assistance experiments How to avoid "ConcurrentModificationException" while removing elements from `ArrayList` while iterating it? For Java 8 and above, you can use the removeIf () method with lambda expressions. [duplicate], Exploring the infrastructure and code behind modern edge functions, Jamstack is evolving toward a composable web (Ep. When to use LinkedList over ArrayList in Java? There is no way to avoid that. Does GDPR apply when PII is already in the public domain? 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. 12 Answers Sorted by: 408 Here is a code sample to use the iterator in a for loop to remove the entry. Or that it will be added for that matter.). On the other hand, if you have say a 'global' queue of metrics snapshots shared among all the requests, each request adds stats to this queue, and some other thread reads the queue elements and deletes the metrics, this way won't be appropriate. Note that I only want to remove elements from the set that are provided by the Iterator. And this is the only way you can modify the collection while iterating. E.g. If I understand your problem correctly, followings would be the possible solutions(might not be most effective but i think is worth a shot): Under performChecks() use for(Object obj : list.toArray()), Advantage: every time the list is "refreshed" to array it will reflect the changes. Why do we say "narrow artificial intelligence" but "artificial general intelligence"? 588), Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g., ChatGPT) is banned. Negative literals, or unary negated positive literals? Edit#1 How to Get Elements By Index from HashSet in Java? Can Loss by Checkmate be Avoided by Invoking the 50-Move Rule Immediately After the 100th Half-Move? Java Iterator remove() Method | Delft Stack Now, I am not fully aware of your exact situation but another option might be to implement hashCode and equals in your Row class, in which case two Row objects with the same properties won't be added to the Set in the first place, and if you want to remove one and replace with another, you can do so with \$O(1)\$ complexity instead of your current \$O(n)\$. This however can only be done using the iterator which is not the case this way. Iterator takes the place of Enumeration in the Java Collections Framework. Difference between List and List