How do I use priority queues in Java?

How do I use priority queues in Java?

You can use the PriorityQueue class in Java, which is part of the Java Collections Framework. It allows you to store elements in a way that the highest (or lowest) priority element can be accessed quickly.

Can you show me a simple example?

Sure! Here's a basic example:

import java.util.PriorityQueue;

public class Main {
    public static void main(String[] args) {
        PriorityQueue<Integer> pq = new PriorityQueue<>();
        pq.add(5);
        pq.add(1);
        pq.add(3);

        while (!pq.isEmpty()) {
            System.out.println(pq.poll()); // prints elements in ascending order
        }
    }
}

What if I want to use custom objects?

You can implement the Comparable interface in your custom class to define the natural ordering. Alternatively, you can provide a Comparator when creating the PriorityQueue.

Can you give an example of using a custom comparator?

Absolutely! Here's an example using a custom comparator:

import java.util.PriorityQueue;
import java.util.Comparator;

class Person {
    String name;
    int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

public class Main {
    public static void main(String[] args) {
        PriorityQueue<Person> pq = new PriorityQueue<>(new Comparator<Person>() {
            public int compare(Person p1, Person p2) {
                return Integer.compare(p1.age, p2.age); // Order by age
            }
        });

        pq.add(new Person("Alice", 30));
        pq.add(new Person("Bob", 25));

        while (!pq.isEmpty()) {
            System.out.println(pq.poll().name); // prints names in order of age
        }
    }
}