Mastering Java Queue Interface and PriorityQueue Class: Unlocking Efficient and Prioritized Data Handling Vaishnavi Tech Talks

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Java Queue Interface and PriorityQueue Class

In Java, the Queue interface and the PriorityQueue class are portion of the Java Collections Framework, giving effective tools for overseeing collections of components with particular ordering and recovery techniques.
Whereas Queue offers a general-purpose interface for working with ordered collections, PriorityQueue expands it with functionality that permits components to be prepared based on their need instead of their insertion order

Java Queue Interface

The Queue interface, part of java.util package, speaks to a collection planned for holding components earlier to preparing.
It is an ordered collection that regularly takes after the first In, First Out (FIFO) principle.
The Queue interface gives strategies for adding, removing, and analyzing components within the collection.

Key highlights of the Queue interface include:

1.FIFO Ordering: Components are retrieved within the order they were added, with the first component added being the first one to be removed.

2.Methods:

add(E e): Inserts the required component into the queue. Throws an IllegalStateException in case the queue is full.
offer(E e): Comparative to add(), but it returns false in case the queue is full rather than throwing an exception.
remove(): Removes and returns the component at the front of the queue. Throws an exception in the event that the queue is empty.
poll(): Removes and returns the component at the front of the queue, or returns invalid in case the queue is empty.
peek(): Returns, but does not remove, the component at the front of the queue, or invalid in case the queue is empty.
element(): Returns the element at the front without removing it, throwing an exception in case the queue is empty.

3.Implementations of Queue:

LinkedList: Implements the Queue interface and supports proficient insertion and removal of components at both ends.
PriorityQueue: A particular implementation of a queue that orders components based on their need.
ArrayDeque: A resizable array implementation of the Deque interface, which moreover works as a queue.

PriorityQueue Class

The PriorityQueue class in Java is a specialized implementation of the Queue interface that orders components based on their need instead of the order in which they were added.
It implements a heap-based priority queue, where the component with the highest (or lowest) priority is continuously at the head of the queue.

Key Highlights of PriorityQueue:

1.Ordering of Elements:

By default, the PriorityQueue orders components agreeing to their natural ordering (ascending arrange for numbers or strings).
You’ll too supply a custom comparator to characterize the order, permitting for descending arrange or any self-assertive order based on your needs.

2.Heap Structure:

Inside, PriorityQueue uses a min-heap structure by default, meaning the smallest component is given the highest priority.
This guarantees productive recovery of the least component in logarithmic time.
In case a custom comparator is given, it can turn the PriorityQueue into a max-heap or any other order based on the comparator’s logic.

3.Important Methods:

add(E e): Adds the required component to the queue.
offer(E e): Adds the required component to the queue, returning false in case the queue is full.
poll(): Retrieves and removes the head of the queue (the component with the highest priority).
peek(): Retrieves but does not remove the head of the queue (the component with the highest priority).
remove(): Removes a particular component from the queue.
comparator(): Returns the comparator utilized to order the components, or invalid in the event that the queue uses the natural ordering.

4.Handling Duplicates:

The PriorityQueue permits duplicate components unless a custom comparator is utilized that explicitly avoids them.

Example of Using PriorityQueue

import java.util.*;

public class PriorityQueueExample {
public static void main(String[] args) {
// Creating a PriorityQueue of integers
PriorityQueue<Integer> queue = new PriorityQueue<>();

// Adding elements to the PriorityQueue
queue.add(10);
queue.add(20);
queue.add(5);
queue.add(15);

// Displaying elements in order of priority (smallest to largest)
System.out.println("PriorityQueue (Min-Heap Order): " + queue);

// Polling elements (removes the smallest element)
System.out.println("Polled element: " + queue.poll()); // Output: 5
System.out.println("PriorityQueue after poll: " + queue);

// Peek at the top element without removing it
System.out.println("Peek at the top element: " + queue.peek()); // Output: 10
}
}

Output:

PriorityQueue (Min-Heap Order): [5, 10, 20, 15]
Polled element: 5
PriorityQueue after poll: [10, 15, 20]
Peek at the top element: 10

In this case, the PriorityQueue is using the natural ordering of integers (min-heap). The smallest component (5) is polled first. After polling, the another smallest component, 10, becomes the head of the queue.

Example of Custom Ordering with Comparator

import java.util.*;

public class PriorityQueueCustomOrder {
public static void main(String[] args) {
// Creating a PriorityQueue with a custom comparator for descending order
PriorityQueue<Integer> queue = new PriorityQueue<>(Collections.reverseOrder());

// Adding elements to the PriorityQueue
queue.add(10);
queue.add(20);
queue.add(5);
queue.add(15);

// Displaying elements in order of priority (largest to smallest)
System.out.println("PriorityQueue (Max-Heap Order): " + queue);

// Polling elements (removes the largest element)
System.out.println("Polled element: " + queue.poll()); // Output: 20
}
}