Queue Remove Method in Java

Introduction

A queue data structure is one of the crucial topics of interviews asked by an interviewer in technical rounds. Due to its principle of first come, first served, it is used where things don't have to be processed easily. There are primarily four basic operations performed on queue: 

• Front, Rear, Enqueue, Dequeue

 

Out of several different queue methods, we will be exploring the remove() method in the Java language. The remove() method removes and returns the element at the front of the pile; it deletes the head of the pile. This method is different from the poll() method as the remove() method throws an exception if the queue is empty.

Also see, Linked Lists

Syntax:-

Parameters: e remove()

Returns: the head of the queue

Throws: NoSuchElementException(When queue is empty)

Example:

Input: 1 2 3 4

Output: 1(returned element)

             2 3 4 (queue after removing the head)

Approach 1: Using ArrayDeque

ArrayDeque provides a resizable array in addition to the implementation of the deque. It implements both queue and deque.

Code

import java.util.*;

public class Solution {
   public static void main(String[] args)
   throws IllegalStateException{

      // using arraydeque
      Queue<Integer> Q = new ArrayDeque<Integer>();

      // Add numbers to end of Queue
      Q.add(7);
      Q.add(3);
      Q.add(5);
      Q.add(6);

      // print queue
      System.out.println("Queue: " + Q);

      // use remove() method
      System.out.println("Queue's head: " + Q.remove());

      // after using the remove() method
      System.out.println("Queue: " + Q);

      // use remove() method
System.out.println("Queue's head: " + Q.remove());
}
}

Output

Queue: [7, 3, 5, 6] Queue's head: 7 Queue: [3, 5, 6] Queue's head: 3

 

Approach 2: LinkedList

The space required for the linked representation of a queue is O(n),where n is the number of elements in the queue, while the time required for operations is O(1).

Code

import java.util.*;

public class Solution {
  public static void main(String[] args)
  throws IllegalStateException{

      // create object of Queue
     Queue<Integer> q = new LinkedList<Integer>();

     // Add numbers to end of Queue
     q.add(7);
     q.add(3);
     q.add(5);
     q.add(4);

     // print queue
     System.out.println("Queue: " + q);

     // print head and deletes the head
     System.out.println("Queue's head: " + q.remove());

     // print queue after using remove() method
     System.out.println("Queue: " + q);
 
    // print head and deleted the head
    System.out.println("Queue's head: " + q.remove());
  }
}

 

Output

Queue: [7, 3, 5, 4] Queue's head: 7 Queue: [3, 5, 4] Queue's head: 3

 

Approach 3: Exception throw method

Code

import java.util.*;

public class Solution {
    public static void main(String[] args)
    throws IllegalStateException{

       // create object of Queue
       Queue<Integer> q = new LinkedList<Integer>();

      // Add numbers to end of Queue
      q.add(7);
      q.add(3);

      // print queue
      System.out.println("Queue: " + q);

      // print head and deletes the head
      System.out.println("Queue's head: " + q.remove());

     // print queue after using the method
     System.out.println("Queue: " + q);

     // print head and deleted the head
    System.out.println("Queue's head: " + q.remove());

    // print queue
    System.out.println("Queue: " + q);

    try {
       // Queue is empty 
       System.out.println("Queue's head: " + q.element());
    }
    catch (Exception e) {
       System.out.println("Exception: " + e);
    }
  }
}

 

Output

Queue: [7, 3] Queue's head: 7 Queue: [3] Queue's head: 3 Queue: [] Exception: java.util.NoSuchElementException

 

Frequently Asked Questions

Difference between stack and queue?

             Stack

• Based on the LIFO principle.
• Insert operation is done by push() method.
• The delete operation is done by the pop() method.
• Insertion and deletion in stacks take place only from one end.

             Queue

• Based on the FIFO principle.
• Insert operation is done by enqueue () method.
• Deletion operation is done by dequeue() method.
• Insertion and deletion in queues take place from the opposite ends of the list.                                      

Different methods to implement remove() method in a queue?

It can be implemented using LinkedList, arraydeque, ConcurrentLinkedDeque.

Difference between remove() and poll() method in queue?

The remove() method throws an exception if the list is empty, which is not in the poll() method.

Conclusion

In this blog, we covered the remove() method of the queue, with their implementation using various approaches in the Java language. You can check out more related to queue data structure for using it in your codes to increase efficiency.

Recommended Readings:

• Advantages of Circular Queue
• How to remove a Specific Element from the Queue
• Queue Data Structure in Java
• Implementation of Queue in Java using Array and Generics
• Difference between Array and Deque in C++
• Love Babbar DSA Sheet
• Striver SDE Sheet Problems

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