Who says java does not supports pointers part-5, implement PriorityQueue using linked list, a code by Vasu

A priority queue is a data structure. 
It is different from  a simple queue, since rather than a 'first in first out' (FIFO) behavior the values in priority queue comes out in order by their priority.

============================================================

This very good code of stack is implemented by 

Vasu Gupta / IT / Maharaja Agrasen Institute of Technology

============================================================

# save this class inside PriorityNode.java file #

import java.util.Scanner;

//Create a PriorityNode class for creating new nodes in linked list
public class PriorityNode{

private String data ;  // data of that node
private int priority ; // Priority of that node
private PriorityNode next ; // node data of next linked node

// initialize new node
public PriorityNode() {
data = null ;
priority = 0 ;
next = null ;
}

// Input data in new node
public PriorityNode(String d , int p , PriorityNode n) {
data = d ;
priority = p ;
next = n ;
}

// set link to the next node
public void setLink(PriorityNode link) {
next = link ;
}

// Get link to the next node
public PriorityNode getLink() {
return next ;
}

// Get data of the current node
public String getData() {
return data ;
}

// Get priority of the current node
public int getPriority() {
return priority ;
}

}

# save this class inside LinkListPriority.java file #

//class for creating linked list
public class LinkListPriority {


private PriorityNode start ;

// Initialize all the variables
public LinkListPriority() {
start = null ;
}

// Adding nodes according to their priority in the queue (Made up of linked list)
public void add(String data , int p) {
PriorityNode node = new PriorityNode(data , p , null);  // Create object of PriorityNode class

PriorityNode p1 ;

if(start == null || node.getPriority() < start.getPriority()) { // Adding first node or placing lower priority node after higher priority node
node.setLink(start);
start = node ;
}else { // Placing nodes according to their priorities . Least at the last of the queue
p1 = start ;
while (p1.getLink() != null && node.getPriority() > p1.getLink().getPriority() && p1.getLink() != null ) {
p1 = p1.getLink();
}

node.setLink(p1.getLink());
p1.setLink(node);

} 
}

// The node having higher priority will be deleted first
public void deleteNode() {

// Check if queue is Empty
if(start == null) {
System.out.println("Empty Queue");
}else {
PriorityNode ptr = start ;
start = start.getLink();
ptr = null ;
}

} 

// Function to show data of the queue
public void showData() {

// Check if queue is Empty
if(start == null) {
System.out.println("No data");
}else {

PriorityNode ptr = start ;

while(ptr.getLink() != null) {
System.out.print(ptr.getData() + "[ P : " + ptr.getPriority() + "]" + "--->");
ptr = ptr.getLink();
}

System.out.print(ptr.getData() + "[ P : " + ptr.getPriority() + "]");

}

}

}


# save this class inside MyPriorityQueue.java file #

public class MyPriorityQueue {

public static void main(String[] args) {

String data ;
int priority ;
LinkListPriority ll = new LinkListPriority();

// Create Scanner class object
Scanner sc = new Scanner(System.in);

// Get user input data again and again
do {
System.out.print("Enter the data : ");
data = sc.next();
System.out.print("Enter the Priority : ");
priority = sc.nextInt();

ll.add(data,priority); // Push the data into the queue

System.out.print("Do you want to add more (y/n) : ");

}while(sc.next().equals("y"));

// Show the data of the queue in priority order
System.out.println("Queue : ");
ll.showData();

// Deleting data of the queue according to their priority
System.out.println("\nQueue after deleting one element");
ll.deleteNode();
ll.showData();

}

}