PriorityBlockingQueue comparator() method in Java

Last Updated : 26 Nov, 2018

The comparator() method of PriorityBlockingQueue returns the comparator that can be used to order the elements in a PriorityBlockingQueue. The method returns null value if the queue follows the natural ordering pattern of the elements.

Syntax:

public Comparator<? super E> comparator()

Returns: This method returns the comparator set used to order the elements of the set in a specific order. It returns a null value if the PriorityBlockingQueue follows the default or natural ordering pattern.

Below programs illustrate comparator() method of PriorityBlockingQueue:

Example 1: To demonstrate comparator() method on PriorityBlockingQueue which contains a list of integers.

// Java Program Demonstrate comparator() 
// method of PriorityBlockingQueue 
  
import java.util.concurrent.PriorityBlockingQueue; 
import java.util.*; 
  
public class GFG { 
    public static void main(String[] args) 
        throws InterruptedException 
    { 
  
        // create object of PriorityBlockingQueue 
        PriorityBlockingQueue<Integer> PrioQueue 
            = new PriorityBlockingQueue<Integer>(); 
  
        // Add numbers to PriorityBlockingQueue 
        PrioQueue.put(45815616); 
        PrioQueue.put(4981561); 
        PrioQueue.put(4594591); 
        PrioQueue.put(9459156); 
  
        // get String representation of PriorityBlockingQueue 
        String str = PrioQueue.toString(); 
  
        // Creating a comparator using comparator() 
        Comparator comp = PrioQueue.comparator(); 
  
        // Displaying the comparator values 
        System.out.println("Comparator value: " + comp); 
  
        if (comp == null) 
            System.out.println("PriorityBlockingQueue"
                               + "follows natural ordering"); 
        else
            System.out.println("PriorityBlockingQueue follows"
                               + comp); 
    } 
} 

Output:

Comparator value: null
PriorityBlockingQueuefollows natural ordering

Example 2: To demonstrate toString() method on PriorityBlockingQueue which contains list of Strings.

// Java Program Demonstrate comparator() 
// method of PriorityBlockingQueue 
  
import java.util.concurrent.PriorityBlockingQueue; 
import java.util.*; 
  
// Comparator to compare Strings 
class COMPARING implements Comparator<String> { 
    public int compare(String str1, String str2) 
    { 
        return str2.compareTo(str1); 
    } 
} 
  
public class GFG { 
    public static void main(String[] args) 
        throws InterruptedException 
    { 
  
        // define capacity of PriorityBlockingQueue 
        int capacityOfQueue = 5; 
  
        // create object of PriorityBlockingQueue 
        // by passing capacity and comparator class 
        // as parameters. 
        PriorityBlockingQueue<String> characters 
            = new PriorityBlockingQueue<String>(capacityOfQueue, 
                                                new COMPARING()); 
  
        // Add Strings 
        characters.add("Geeks"); 
        characters.add("forGeeks"); 
        characters.add("A computer portal"); 
  
        // Getting the comparator using comparator() 
        Comparator comp = characters.comparator(); 
  
        // Displaying the comparator values 
        System.out.println("Comparator value is: " + comp); 
  
        if (comp == null) 
            System.out.println("PriorityBlockingQueue"
                               + "follows natural ordering"); 
        else
            System.out.println("PriorityBlockingQueue follows: "
                               + comp); 
        // display result 
        System.out.println("\nThe elements after custom Comparator"); 
        for (String e : characters) 
            System.out.print(e + ", "); 
    } 
} 

Output:

Comparator value is: COMPARING@28d93b30
PriorityBlockingQueue follows: COMPARING@28d93b30

The elements after custom Comparator
forGeeks, Geeks, A computer portal,

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/PriorityBlockingQueue.html#comparator–

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