![]() ![]() Short of seeing the code, that's about as good as I can do.Īfter your update that you were indeed using LinkedList, I thought I'd give it a shot with a very simple example xx.java: import java.util. Remove an element from a Queue in Java - To remove an element from a Queue, use the remove() method.First, set a Queue and insert some elements Queue q new LinkedList() q.offer(abc) q.offer(def) q.offer(ghi) q.offer(jkl) q.offer(mno) q.offer(pqr) q.offer(stu) q. The second and most likely is that you're not removing the element from the queue when you call remove, rather you're returning the string without adjusting whatever your underlying data structure is (or, alternatively, adjusting it wrongly). This is far more likely in a language like C where you may inadvertently reuse the same pointer but it's far less likely in Java with its improved strings. Since null is used as a special value, its worth. The first is that you are somehow setting each node of your queue to the same value and you may well be removing items okay (you can detect this by adding one item then trying to remove two). Similarly poll() returns null if the queue is empty, while the remove method throws an unchecked exception. Let's outline a few of the more important ones now: offer () Inserts a new element onto the Queue poll () Removes an element from the front of the Queue peek () Inspects the element at the front of the Queue, without removing it 4. If, on the other hand, you've implemented your own queue then, yes, there may well be a problem but, since psychic debugging is not yet a well-established field of endeavour, you're going to have to show us the code for it :-) Core Methods The Queue declares a number of methods that need to be coded by all implementing classes. well, close enough to zero that we can discount it as a possibility. Depending on what language you are using, you may be able to take some shortcuts.If myQueue is an instance of a standard Java class implementing the Queue interface, the chance that you have found a bug with it are. ![]() So if we have a LinkedList rather than a Queue, we can simply list.remove(indexOfTheMiddleElement). I cannot find any usages outside of the JDK. The Basics enqueue(x) : add an item at the tail dequeue : remove the item at the head peek : return the item at the head (without removing it) size : return. If we have access to such implementation details of a queue, we can splice out the element more easily. Java SE has had support for Queues in Collections for many major releases, seems to predate that. Some implementations of queues are actually fully-featured linked lists (e.g. For a stack, we usually call enqueue push and dequeue pop. Exactly which element is removed from the queue is a function of the queues ordering policy, which differs from implementation to implementation. ![]() In fact, most Queues we'll encounter in Java work in this first in, first out manner often abbreviated to FIFO. Of course, this only works if the input queue is not changed while this algorithm is executed.įor LIFO queues (i.e., stacks), we only have to remove half of the elements as we can replay the items in the correct order. The remove () and poll () methods remove and return the head of the queue. After we declare our Queue, we can add new elements to the back, and remove them from the front. īut replaying the removed items in the correct order requires us to remove all elements, since we cannot push items back onto the end! We have to do something like this: val q: Queue =. Getting and removing the middle element is trivial by also removing all earlier elements: val q: Queue =. ![]() Let's look at the case of a FIFO queue that only supports these two operations and additionally has a size property. It retrieves, but does not remove, the head of the priority queue, and throws NoSuchElementException if the queue is empty. So in the general case, we can't use any other functions. Queues are generally considered to be an abstract data type that only has enqueue and dequeue operations. ![]()
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