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Dynamic Queue implementation using arrays
A queue is a kind of abstract data type or collection in which the entities in the collection are kept in order and the
only operations on the collection are the addition of entities to the rear terminal position, called as enqueue, and removal of entities
from the front terminal position, called as dequeue. The queue is called as First-In-First-Out (FIFO) data structure. In a FIFO data
structure, the first element added to the queue will be the first one to be removed. You can find more details in the previous example
Here you can find dynamic queue implementation based on array. The capacity of the array will be increased when
the queue is full.
package com.java2novice.ds.queue;
public class DynamicQueueImpl {
private int capacity = 2;
int queueArr[];
int front = 0;
int rear = -1;
int currentSize = 0;
public DynamicQueueImpl(){
queueArr = new int[this.capacity];
}
/**
* this method adds element at the end of the queue.
* @param item
*/
public void enqueue(int item) {
if (isQueueFull()) {
System.out.println("Queue is full, increase capacity...");
increaseCapacity();
}
rear++;
if(rear >= queueArr.length && currentSize != queueArr.length){
rear = 0;
}
queueArr[rear] = item;
currentSize++;
System.out.println("Adding: " + item);
}
/**
* this method removes an element from the top of the queue
*/
public void dequeue() {
if (isQueueEmpty()) {
System.out.println("Underflow ! Unable to remove element from Queue");
} else {
front++;
if(front > queueArr.length-1){
System.out.println("removed: "+queueArr[front-1]);
front = 0;
} else {
System.out.println("removed: "+queueArr[front-1]);
}
currentSize--;
}
}
/**
* This method checks whether the queue is full or not
* @return boolean
*/
public boolean isQueueFull(){
boolean status = false;
if (currentSize == queueArr.length){
status = true;
}
return status;
}
/**
* This method checks whether the queue is empty or not
* @return
*/
public boolean isQueueEmpty(){
boolean status = false;
if (currentSize == 0){
status = true;
}
return status;
}
private void increaseCapacity(){
//create new array with double size as the current one.
int newCapacity = this.queueArr.length*2;
int[] newArr = new int[newCapacity];
//copy elements to new array, copy from rear to front
int tmpFront = front;
int index = -1;
while(true){
newArr[++index] = this.queueArr[tmpFront];
tmpFront++;
if(tmpFront == this.queueArr.length){
tmpFront = 0;
}
if(currentSize == index+1){
break;
}
}
//make new array as queue
this.queueArr = newArr;
System.out.println("New array capacity: "+this.queueArr.length);
//reset front & rear values
this.front = 0;
this.rear = index;
}
public static void main(String a[]){
DynamicQueueImpl queue = new DynamicQueueImpl();
queue.enqueue(4);
queue.dequeue();
queue.enqueue(56);
queue.enqueue(2);
queue.enqueue(67);
queue.dequeue();
queue.enqueue(24);
queue.enqueue(98);
queue.dequeue();
queue.dequeue();
queue.dequeue();
queue.enqueue(435);
queue.dequeue();
queue.dequeue();
}
}
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| Output: |
Adding: 4
removed: 4
Adding: 56
Adding: 2
Queue is full, increase capacity...
New array capacity: 4
Adding: 67
removed: 56
Adding: 24
Adding: 98
removed: 2
removed: 67
removed: 24
Adding: 435
removed: 98
removed: 435
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List of Queue Data Structure Examples
- Queue introduction & array based implementation
- Dynamic Queue implementation using arrays
- Double-ended queue (Decue) Implementation
- Double-ended queue (Decue) implementation using Doubly linked list
- Priority Queue introduction and Java implementation
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What is System.out in Java
In System.out, out is an instance of PrintStream. It is a static member variable in
System class. This is called standard output stream, connected to console.
Tomorrow is often the busiest day of the week.
-- Spanish Proverb
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