Priority Queue of Pair in Java with Examples

In Java, a priority queue of pairs can be implemented using the PriorityQueue class and the Pair class from the javafx.util package. Here are two methods to implement a priority queue of pairs in Java:

Method 1: Using a Comparator

In this method, we create a Comparator object that compares pairs based on their first element. We then create a PriorityQueue object and pass the Comparator object as a parameter to its constructor. We can then add pairs to the priority queue using the add() method, and remove the pair with the highest priority using the poll() method.

Example:

import javafx.util.Pair;
import java.util.Comparator;
import java.util.PriorityQueue;

public class PriorityQueueExample {
    public static void main(String[] args) {
        // Create a Comparator object that compares pairs based on their first element
        Comparator<Pair<Integer, String>> comparator = new Comparator<Pair<Integer, String>>() {
            @Override
            public int compare(Pair<Integer, String> p1, Pair<Integer, String> p2) {
                return p1.getKey().compareTo(p2.getKey());
            }
        };

        // Create a PriorityQueue object and pass the Comparator object as a parameter to its constructor
        PriorityQueue<Pair<Integer, String>> pq = new PriorityQueue<>(comparator);

        // Add pairs to the priority queue
        pq.add(new Pair<>(3, "Alice"));
        pq.add(new Pair<>(1, "Bob"));
        pq.add(new Pair<>(2, "Charlie"));

        // Remove the pair with the highest priority
        Pair<Integer, String> highestPriorityPair = pq.poll();
        System.out.println(highestPriorityPair.getValue()); // Output: "Bob"
    }
}

Method 2: Using Comparable

In this method, we make the Pair class implement the Comparable interface and define the compareTo() method to compare pairs based on their first element. We can then create a PriorityQueue object and add pairs to it using the add() method, and remove the pair with the highest priority using the poll() method.

Example:

import javafx.util.Pair;
import java.util.PriorityQueue;

public class PriorityQueueExample {
    public static void main(String[] args) {
        // Create a PriorityQueue object
        PriorityQueue<Pair<Integer, String>> pq = new PriorityQueue<>();

        // Add pairs to the priority queue
        pq.add(new Pair<>(3, "Alice"));
        pq.add(new Pair<>(1, "Bob"));
        pq.add(new Pair<>(2, "Charlie"));

        // Remove the pair with the highest priority
        Pair<Integer, String> highestPriorityPair = pq.poll();
        System.out.println(highestPriorityPair.getValue()); // Output: "Bob"
    }
}

// Make the Pair class implement the Comparable interface
class Pair<K extends Comparable<? super K>, V> implements Comparable<Pair<K, V>> {
    private final K key;
    private final V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() {
        return key;
    }

    public V getValue() {
        return value;
    }

    // Define the compareTo() method to compare pairs based on their first element
    @Override
    public int compareTo(Pair<K, V> other) {
        return this.key.compareTo(other.key);
    }
}