![]() ![]() ![]() Heres a thought experiment for you to go through. Note: It is not recommended to use ArrayList.remove () when iterating over elements. If you think about how the computer has to reconcile it, it makes sense. There are 3 ways to remove an element from ArrayList as listed which later on will be revealed as follows: Using remove () method by indexes (default) Using remove () method by values. When we use the enhanced for loop, there is a call to a method iterator() in the ArrayList when the for loop is going to be executed. It is problematic to iterate over a list and remove elements while iterating over it. ArrayList implements the Iterator interface via a private inner class, Itr. remove(Object o).īut from a technical perspective, what is happening behind the scenes?Įven though we are using an enhanced for loop, there is an Iterator involved behind the scenes. The moment you see the word Concurrent, you are thinking, why I am getting this exception, I am not using threads ! Note that while iterating using the enhanced for loop we are also trying to remove elements, which means we are modifying the structure of the list while we are iterating. Exception in thread "main" at $Itr.checkForComodification(ArrayList.java:901) at $Itr.next(ArrayList.java:851) at (RemoveItems.java:52) at (RemoveItems.java:27) But on running this, we get a ConcurrentModificationException. remove () is one of Python's built-in list methods. The general syntax of the remove () method looks like this: listname.remove(value) Let's break it down: listname is the name of the list you're working with. To fix this, you should not increment the loop index within an iteration in which you have just removed an element. The remove () method removes an item from a list by its value and not by its index number. But this is wrong because if you have just removed an element, youll end up skipping the following element. So, if you remove at (or before) the current index, everything from that point until the end shifts one spot to the left. ![]() Well, the code looks quite straightforward. You are incrementing the loop index at the end of each loop iteration. List iteration works by keeping track of an index, incrementing it each time around the loop until it falls off the end of the list. next (): The next () method perform the iteration in forward order. Now, lets see an example of removing elements from ArrayList while looping using for () loop and ArrayList. It contains two key methods next () and hasNaxt () that allows us to perform an iteration over the List. There are 7 ways you can iterate through List. Java provides an interface Iterator to iterate over the Collections, such as List, Map, etc. The initialize method adds some data to the ArrayList. How to iterate through Java List This tutorial demonstrates the use of ArrayList, Iterator and a List. Take a look at the removeIllegalUsingEnhancedForLoop method which uses the enhanced for loop. ![]()
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