How do I modify elements of PriorityQueue in Java?

Normally, queues follow the first-in-first-out (FIFO) principle, but PriorityQueue A priority-based approach is followed when accessing elements in a priority manner. each element of the queue Has a priority associated with it. Elements are prioritized according to their natural ordering order. However, we can provide custom orders using a comparator. The elements of PriorityQueue are not actually sorted, they are only retrieved in sorted order. This feature allows us to modify an element of PriorityQueue easily.

Java Program to modify an element of a ProrityQueue

Before starting the program, let us first understand several built-in methods of PriorityQueue -

• add() − It is used to add a single element to the queue

• offer() − It also inserts the given element into the queue.

• peek() − Used to retrieve the first element of the queue.

• remove() − It is used to remove the specified element from the queue.

Approach 1

• Define a PriorityQueue collection object and use the 'add()' method to store some elements

method.

• Now, using ‘peek()’ method show the first element of queue and then remove this Remove elements from the queue using the 'remove()' method

• Move further and insert a new element at the same position using built-in methods

‘offer()’.

• Again show the modified first element.

Example

Example

In the following example, we will modify an element of PriorityQueue. The elements are

There is no priority for the comparators, which means they will be accessed in ascending order.

import java.util.*;
public class Modify {
  public static void main(String[] args) {
      PriorityQueue<Integer> queuePq = new PriorityQueue<>();
      
      // inserting elements
      queuePq.add(7);
      queuePq.add(9);
      queuePq.add(2);
      queuePq.add(4);
      queuePq.add(3);
      
      System.out.println("Original Queue: " + queuePq);
      int head1 = queuePq.peek(); // accessing first element
      
      System.out.println("The first element in Queue: " + head1);
      queuePq.remove(2); // removing first element
      queuePq.offer(1); // adding new element at first position
      int head2 = queuePq.peek(); // accessing first element
      
      System.out.println("The updated first element in Queue: " + head2);
      queuePq.offer(2); // adding new element at first position
      System.out.println("Newly updated Queue: " + queuePq);
   }
}

Output

Original Queue: [2, 3, 7, 9, 4]
The first element in Queue: 2
The updated first element in Queue: 1
Newly updated Queue: [1, 3, 2, 9, 4, 7]

Method Two

• Define an object of the PriorityQueue collection using a built-in method named ‘Collections.reverseOrder()’ is used to store elements in descending order.

• Now, follow the same steps described in the previous example.

Example

Example

In the following example, we will modify an element of PriorityQueue. The elements are Use a comparator for prioritization to provide access in descending order.

import java.util.*;
public class Modify {
   public static void main(String[] args) {
      PriorityQueue<Integer> queuePq = new
      PriorityQueue<>(Collections.reverseOrder());
      
      // inserting elements
      queuePq.add(7);
      queuePq.add(9);
      queuePq.add(2);
      queuePq.add(1);
      queuePq.add(3);
      
      System.out.println("Original Queue: " + queuePq);
      int head1 = queuePq.peek(); // accessing first element
      
      System.out.println("The first element in Queue: " + head1);
      queuePq.remove(9); // removing first element
      queuePq.offer(8); // adding new element at first position
      int head2 = queuePq.peek(); // accessing first element
      
      System.out.println("The updated first element in Queue: " + head2);
      queuePq.offer(9); // adding new element at first position
      System.out.println("Newly updated Queue: " + queuePq);
   }
}     

Output

Original Queue: [9, 7, 2, 1, 3]
The first element in Queue: 9
The updated first element in Queue: 8
Newly updated Queue: [9, 7, 8, 1, 3, 2]

in conclusion

We start this article by defining the PriorityQueue class of the Java Collection Framework Implement the content of the Queue interface. In the next section we'll discuss some of the built-in Method used in Java program to modify elements in given PriorityQueue

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