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PriorityQueue, LinkedList as Queue

In Java programming, both PriorityQueue and LinkedList data types can be implemented in Java programs as the Queue/List interface. The default usage behavior, use cases, and system performance specifications and features of both PriorityQueue and LinkedList data types in Java differ in individual ordering.

So, let’s take a closer look at both PriorityQueue and LinkedList data types in Java programming.

PriorityQueue in Java.

The PriorityQueue data type in the Java programming language is a built-in feature of the Java Collection Framework. It helps Java users implement the Queue interface data type structure in programs. It is defined as a queue data structure that orders its data elements in a queue according to their default natural order or according to a custom comparator provided at the time of queue data element creation. In this, the queue element with the highest priority is always represented first, or at the top, of the queue. This differs from a regular FIFO (first-in-first-out) queue order.

Special features of Java PriorityQueue.

• Priority-based ordering – It orders or arranges Java queue elements according to their set priority, such as natural order or a custom user-defined comparator. In the queue data order, the queue element with the highest priority is dequeued first.
• Not FIFO – Unlike traditional queues, PriorityQueue is not mandatory in the Java Queue data type. Here, queue elements are dequeued in the same order in which they were added. This queue order depends on the priority of the added data element.
• Null values ​​​​not allowed – Priority queues in Java programs do not allow null value elements because the queue priority is defined by a comparator or natural ordering.
• Not synchronized – The Queue data type element in a Java program does not have thread-safe features by default. If the Java user requires thread-safety features, the Java user will need to implement external synchronization or implement a PriorityBlockingQueue in a concurrent environment.
• Performance – In a Java program, Queue function method operations such as add(), remove(), and peek() typically use O(log n) time due to the underlying heap data structure.

Java PriorityQueue Example.

import java.util.PriorityQueue;

public class PriorityDataType {

public static void main(String[] args) {

// here we are creating a PriorityQueue with a natural data element order/min-heap by default.

PriorityQueue<Integer> pqdata = new PriorityQueue<>();

// here we Adding a desire numeric elements to the PriorityQueue data type

pqdata.add(11);

pqdata.add(12);

pqdata.add(13);

pqdata.add(14);

pqdata.add(15);

// here we Removing and printing elements from the PriorityQueue data element

System.out.println(“Here Priority Queue elements is -“);

while (!pqdata.isEmpty()) {

System.out.println(pqdata.poll()); // here it PriorityQueue Elements are dequeued in the order of their priority arrange smallest first

}

}

}

Java PriorityQueue Explanation.

In the PriorityQueue example here, the smallest priority queue element (11) is dequeued first because PriorityQueues by default follow the min-heap concept ordering, where the queue element with the lowest value has the highest priority. If Java users want max-heap features, where larger queue elements have higher priority, they can use a custom comparator.

LinkedList as a Queue in Java.

In Java programs, the LinkedList data type is a doubly-linkedlist implementation of the List data type interface. Remember, the LinkedList data type implements the Queue data interface. Because of this, it can be implemented as a queue. A LinkedList used as a queue follows the FIFO (First In First Out) concept. Here in this use LinkedList elements are added from the back of the queue, and deleted from the front LinkedList order.

Features of LinkedList as a Queue.

• FIFO ordering – A linked list used as a queue maintains the order in which new data elements are inserted into the data. The first list element added to the linked list is the first to be removed from the list (FIFO) order.
• Flexible – A linked list queue in Java programs allows data operations such as offer(), poll(), peek(), and list operations such as add(), get(), and remove().
• Allows null values ​​- Unlike the Java PriorityQueue, Java users can store a null element in a linked list data type. However, some queue implementation methods may block.
• Not synchronized – Unlike the Collection class, a linked list data type is not synchronized, so thread-safety features are required if the linked list data type requires them. So Java users will have to manage this order externally or use a variant that runs concurrently.

Java LinkedList as a Queue example.

import java.util.LinkedList;

import java.util.Queue;

public class LinkedListDataType {

public static void main(String[] args) {

// Here we are creating a LinkedList as a Queue data type

Queue<String> queuedata = new LinkedList<>();

// Here we are enqueuing/adding LinkedList elements to the rear of the queue data

queuedata.offer(“Java”);

queuedata.offer(“Python”);

queuedata.offer(“Sql”);

queuedata.offer(“Matlab”);

// Here we are dequeuing LinkedList elements/removing them from the front of the queuedata element.

System.out.println(“Here is the sequence of deletion of the Queue elements -“);

while (!queuedata.isEmpty()) {

System.out.println(queuedata.poll()); // Here, LinkedList elements are dequeued in the FIFO sequence order.

}

}

}

LinkedList as a Queue explanation.

In the LinkedList example here, LinkedList elements are dequeued in the same order they were enqueued into the LinkedList. First comes Java, followed by Python, SQL, and Matlab, Sequence, etc.

Main difference between PriorityQueue and LinkedList as Queue

Summary of the use of PriorityQueue and LinkedList in Java.

• PriorityQueue – The PriorityQueue data type is used in Java programming when the Java user needs to dequeue PriorityQueue elements based on priority rather than insertion order. For example, when the Java user applies priority scheduling algorithms such as CPU scheduling or task priority.
• LinkedList as a Queue – The LinkedList data type is used in Java programming when the Java user needs a standard FIFO queue sequence order. For example, when LinkedList tasks or messages are maintained or processed in the same sequence order as the LinkedList data order in which they were received. This makes the LinkedList data type very useful for event handling, buffering, or any similar situation where the first LinkedList data element added to the LinkedList data must be processed first.