Convert a Queue to List

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What is the fastest way to convert a Queue into a List while keeping the Queue order?

The fastest is to use a LinkedList in the first place which can be used as a List or a Queue.

Queue q = new LinkedList();
List l = (List) q;

Otherwise you need to take a copy

List l = new ArrayList(q);

Convert a Queue to a List in Java, In order to convert a Queue to a List in Java, we can create an LinkedList and pass the Queue as an argument in the parameterized constructor  Convert a Queue to a List in Java Java 8 Object Oriented Programming Programming In order to convert a Queue to a List in Java, we can create an LinkedList and pass the Queue as an argument in the parameterized constructor of an ArrayList. This can be done as follows −

Pass Queue To ArrayList Constructor

The easiest way to just create a ArrayList and pass your Queue as an argument in the constructor of ArrayList that takes a Collection. A Queue is a Collection, so that works.

This is the easiest way and I believe fastest way too.

List<?> list = new ArrayList<>( myQueue );

Java Collection, PriorityQueue Exercises: Convert a priority queue to , Write a Java program to convert a priority queue to an array containing Priority Queue: "+pq1); //Convert a linked list to array list List<String>  Priority queue: 2. Queue data structure: 3. Create a queue using LinkedList class: 4. Simple Queue (FIFO) based on LinkedList: 5. The Generic Queue Class: 6. Blocking Queue: 7. Circular Queue: 8. Circular Queue extends AbstractList: 9. How to extend the collections framework: 10. An unbounded {@link TransferQueue} based on linked nodes. 11.

Queue queue = new LinkedList();
...
List list = new ArrayList(queue);

Convert a Queue to a List : Queue « Collections Data Structure « Java, Convert a Queue to a List import java.util.ArrayList; import java.util.LinkedList; import java.util.List; import java.util.Queue; public class Main { public static void  Queue outputQueue = new LinkedList(); List list = (List)outputQueue; Weather or not this is a better way to do what you need depends on how you are using the List. You have to decide if the cost of create a new ArrayList is worth the the potential speed increase in accessing your data.

Google:

Queue fruitsQueue = new LinkedList();
fruitsQueue.add("Apples");
fruitsQueue.add("Bananas");
fruitsQueue.add("Oranges");
fruitsQueue.add("Grapes");

List fruitsList = new ArrayList(fruitsQueue);

C#, When you add an item in the list, it is called enqueue, and when you remove an item, it is called deque. Queue .ToArray Method is used to copy the Queue  If you're converting from PriorityQueue to a List, remember that it is in fact a heap, so the ordering is determined using the poll() method. The above methods won't preserve the natural ordering of the queue.

Answering to old question for users who are already on java 8 Java 8 provides the option of using streams and you can get a list from queue as:

For example:

Queue<Student> queue = new LinkedList<>();
        Student s1 = new Student("A",2);
        Student s2 = new Student("B",1);
        Student s3 = new Student("C",3);
        queue.add(s1);
        queue.add(s2);
        queue.add(s3);

    List<Student> studentList = queue.stream().collect(Collectors.toCollection(ArrayList::new));

PriorityQueue toArray() Method in Java, Basically, it copies all the element from a priority queue to a new array. Syntax: Object[] arr = Priority_Queue.toArray(). Parameters: The method does not take any  The Queue<T> class implements, IEnumerable <T>, IEnumerable and ICollection interfaces. Like LinkedList<T>, Queue<T> doesn’t implement the IList<T> and IList interface due to the reason that index operations are not supported by queues. Now, as always, let us explain Queue<T> class with the help of a working example. Have a look at Example4

Java Queue – Queue in Java, Collection interface. Just like Java List, Java Queue is a collection of. Here we can explore how to convert a Java array to Queue using “Collections.addAll()”  In the previous post, we introduced Queue and discussed array implementation. In this post, linked list implementation is discussed. The following two main operations must be implemented efficiently. In a Queue data structure, we maintain two pointers, front and rear. The front points the first item of queue and rear points to last item.

Stacks and Queues in Python, Stacks and Queues using Lists. Python's built-in List data structure comes bundled with methods to simulate both stack and queue operations. Let's consider a  The java.util.PriorityQueue.toArray() method in Java is used to form an array of the same elements as that of the Priority Queue. Basically, it copies all the element from a priority queue to a new array. Syntax: Object[] arr = Priority_Queue.toArray() Parameters: The method does not take any parameters.

ProjPython – Stacks, queues, and dictionaries, If you dequeue an item a queue by deleting an item from the front of a list, the To convert the key to a hash code, Python uses a hash function that takes the  A queue can be implemented using two stacks. Let queue to be implemented be q and stacks used to implement q be stack1 and stack2. q can be implemented in two ways: Recommended: Please solve it on “ PRACTICE ” first, before moving on to the solution. Method 1 (By making enQueue operation costly) This method makes sure that oldest entered

Comments
  • q.poll(), list.add() ?
  • FYI this has issues when used with PriorityQueue read this [Hacker Rank Case](hackerrank.com/challenges/java-priority-queue/forum/comments/… ) you will have to poll with loop to get it right in the list
  • @shareef I'm having the same issue. Took the whole evening for an actually easy problem.
  • Should be the accepted answer, is it is the only one to directly address the Question. The Question referred to the Queue interface. There are many implementations of Queue, both bundled with Java and found in other libraries such as Google Guava. The other answers refer only to LinkedList which is but one of many implementations.