Tag Archives: queue

What is Queue?

Queues are dynamic collections which have some concept of order. This can be either based on order of entry into the queue - giving us First-In-First-Out (FIFO) or Last-In-First-Out (LIFO) queues. Both of these can be built with linked lists: the simplest "add-to-head" implementation of a linked list gives LIFO behaviour. A minor modification - adding a tail pointer and adjusting the addition method implementation - will produce a FIFO queue.

Queue Implementation

package queue

import java.util.Scanner;

public class Queue {

int[] arr = new int[10];
int a = -1;
int b=0;
public void enqueue(int i){

if(a==9){

System.out.println("Queue is full");

}

else
arr[++a]=i;

}
public void dequeue(){

if(a>b){

for(b=0; b

arr[b]=arr[b+1];

}
a--;
b=0;
}

}

public void display(){

for(int i=0; i<=9; i++){

System.out.println("values at index "+i+":"+arr[i]);

}

}

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);
Queue q = new Queue();
int var = -1;
while( var !=0 ){

System.out.println("1. Insert item in queue");
System.out.println("2. Delete item from queue");
System.out.println("3. Display Queue");
System.out.println("0. Exit");
var = sc.nextInt();
switch(var){

case 1:
System.out.print("Enter item in Queue: ");
int pushItem = sc.nextInt();
q.enqueue(pushItem);
break;
case 2:

q.dequeue();
break;
case 3:
q.display();
break;
}
}

}
}