A priority queue is a special type of queue that orders elements based on their priority. Elements with higher priority are dequeued before lower-priority elements. PriorityQueue uses a heap data structure internally to provide efficient O(log n) time for enqueue and dequeue operations.

In this article, we will learn how to convert an ArrayList and an Array into a PriorityQueue in Java.

Syntax of converting an ArrayList into a PriorityQueue:

ArrayList<T> arrayList = new ArrayList<>();
PriorityQueue<T> priorityQueue = new PriorityQueue<>(arrayList);

Program to Convert an ArrayList into a PriorityQueue in Java

Below is the implementation to convert an ArrayList into a PriorityQueue Java.

import java.util.ArrayList;
import java.util.PriorityQueue;

public class Main {
    public static void main(String[] args)
    {
        // create an ArrayList
        ArrayList<String> courseList = new ArrayList<>();
        courseList.add("C++");
        courseList.add("Java");
        courseList.add("Python");

        // convert ArrayList to PriorityQueue
        PriorityQueue<String> queue
            = new PriorityQueue<>(courseList);

        // print PriorityQueue
        for (String str : queue) {
            System.out.print(str + " ");
        }
    }
}

C++ Java Python 

Explanation of above code:

• An ArrayList of courses created.
• Then it converted to PriorityQueue using constructor.
• For-each loop iterates PriorityQueue.
• Elements printed separated by space.

Syntax of converting an Array into a PriorityQueue:

T[] array = { /* elements of the arary */ };
PriorityQueue<T> priorityQueue = new PriorityQueue<>(Arrays.asList(array));

Program to Convert an Array into a PriorityQueue in Java

Below is the implementation to convert an Array into a PriorityQueue Java

// Java Program to Convert an Array into a PriorityQueue
import java.util.Arrays;
import java.util.PriorityQueue;

public class Main {
    public static void main(String[] args)
    {
        // create an Array
        String[] courseArray = { "C++", "Java", "Python" };

        // convert Array to PriorityQueue
        PriorityQueue<String> queue = new PriorityQueue<>(
            Arrays.asList(courseArray));

        // print PriorityQueue
        for (String str : queue) {
            System.out.print(str + " ");
        }
    }
}

C++ Java Python 

Explanation of above code:

• The array of strings {"C++", "Java", "Python"} is converted to a PriorityQueue using Arrays.asList().
• A PriorityQueue orders elements in ascending natural order by default.
• So, when iterating over the PriorityQueue, the elements will be in order of their ASCII values - "C++", "Java", "Python".
• Therefore, the output printed will be: C++ Java Python.