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PriorityQueue remove() Method in Java

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  • Difficulty Level : Medium
  • Last Updated : 14 Dec, 2021
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The remove() method of PriorityQueue class of java.util package is used to remove a particular element from a PriorityQueue. As we all know that the elements while entering into the priority queue are not sorted but as we all know while taking out elements from the priority queue the elements are always sorted being a trait of the priority queue. Here the default ordering of priority of elements for data types is defined as follows:

  • Integer: Smallest elements that come first (while dealing with positive numbers only)
  • String: Alphabetical ordering

Note: We can also insert a Comparator while creating an instance of this class which tells us how the priority should be defined.

Syntax:

PriorityQueue<String> = new PriorityQueue<String>(ComparatorHere);

Syntax: Remove method  

Priority_Queue.remove(Object O)

Parameters: The parameter O is of the type of PriorityQueue and specifies the element to be removed from the PriorityQueue.

Return Value: This method returns True if the specified element is present in the Queue else it returns False.

Example 1

Java




// Java Program to Illustrate remove() Method
// in PriorityQueue
// Where Elements are of String Type
 
// Importing all utility classes
import java.util.*;
 
// Main class
// PriorityQueueDemo
public class GFG {
 
    // Main driver method
    public static void main(String args[])
    {
 
        // Creating an empty PriorityQueue
        // where elements are of string type
        PriorityQueue<String> queue
            = new PriorityQueue<String>();
 
        // Adding elements into the Queue
        // using add() method
        queue.add("Welcome");
        queue.add("To");
        queue.add("Geeks");
        queue.add("For");
        queue.add("Geeks");
 
        // Printing the elements of PriorityQueue
        System.out.println("Initial PriorityQueue: "
                           + queue);
 
        // Removing elements from PriorityQueue
        // using remove() method
        queue.remove("Geeks");
        queue.remove("For");
        queue.remove("Welcome");
 
        // Displaying the PriorityQueue
        // after removal of element
        System.out.println("PriorityQueue after removing "
                           + "elements: " + queue);
    }
}

Output

Initial PriorityQueue: [For, Geeks, To, Welcome, Geeks]
PriorityQueue after removing elements: [Geeks, To]

 Example 2 

Java




// Java Program to Illustrate remove() Method
// of PriorityQueue class
// Where Elements are of Integer type
 
// Importing required classes
import java.util.*;
 
// Main class
// PriorityQueueDemo
public class GFG {
 
    // Main driver method
    public static void main(String args[])
    {
 
        // Creating an empty PriorityQueue by
        // creating an object of integer type
        PriorityQueue<Integer> queue
            = new PriorityQueue<Integer>();
 
        // Adding custom input elements
        // using add() method
        queue.add(10);
        queue.add(15);
        queue.add(30);
        queue.add(20);
        queue.add(5);
 
        // Displaying the PriorityQueue
        System.out.println("Initial PriorityQueue: "
                           + queue);
 
        // Removing elements from the PriorityQueue
        // using remove() method
        queue.remove(30);
        queue.remove(5);
 
        // Displaying the PriorityQueue elements
        // after removal
        System.out.println("PriorityQueue after removing "
                           + "elements: " + queue);
    }
}

Output: 

Initial PriorityQueue: [5, 10, 30, 20, 15]
PriorityQueue after removing elements: [10, 20, 15]

 

Geek, have you ever wondered what will happen if calls of remove() method exceed the elements present in the queue. In this scenario, it will continue to remove the elements that were there, and thereafter it will not find any element to remove priority-wise, so it will throw an exception which is as follows.

Note: This class do implements AbstractQueueInterface

Example 

Java




// Java Program to illustrate remove() Method
// in PriorityQueue
// Where Exception is encountered
 
// Importing required classes
import java.io.*;
import java.util.PriorityQueue;
 
// Main class
// PriorityQueueException
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
 
        // Creating an empty PriorityQueue
        PriorityQueue<Integer> pq
            = new PriorityQueue<Integer>();
 
        // Note: Elements are inserted in unsorted order in
        // priority queue but after removal of elements
        // queue is always sorted.
 
        // Adding elements in above queue
        // using add() method
        pq.add(2);
        pq.add(14);
        pq.add(41);
        pq.add(7);
        pq.add(99);
 
        // Elements in queue are unsorted by far
 
        // Getting size of above queue before deletion
        // of any element using size() method
        System.out.println(
            "Size of priority queue before deletion : "
            + pq.size());
 
        // Printing all elements of above queue
        System.out.println(
            "Priority queue before removal : " + pq);
 
        // Calling remove() method over priority queue
        // in which there were 5 elements
 
        // Here calling remove() method say be it 2 times
        // So 2 top priority elements will be removed
        System.out.println(" 1st element removed : "
                           + pq.remove());
        System.out.println(" 2nd element removed : "
                           + pq.remove());
        System.out.println(" 3rd element removed : "
                           + pq.remove());
        System.out.println(" 4th element removed : "
                           + pq.remove());
        System.out.println(" 5th element removed : "
                           + pq.remove());
 
        // By now queue is empty and if now we made further
        // remove() call it will throw exception for this
        System.out.println(" 6th element removed : "
                           + pq.remove());
 
        // As we know smaller the integer bigger the
        // priority been set by default comparator of this
        // class
 
        // Note: Now the element is always returned sorted
        // from a priority queue is a trait of this class
 
        // Printing the queue after removal of priority
        // elements
        System.out.println(
            "Priority queue after removal as follows: "
            + pq);
    }
}

Output:

Output explanation:

It is showcasing that there are no further elements left in the queue as a queue is empty by now so does it throw NoSuchElementException.


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