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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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When to use LinkedList or ArrayList?
Accessing elements are faster with ArrayList, because it is index based.
But accessing is difficult with LinkedList. It is slow access. This is
to access any element, you need to navigate through the elements one by
one. But insertion and deletion is much faster with LinkedList, because
if you know the node, just change the pointers before or after nodes.
Insertion and deletion is slow with ArrayList, this is because, during
these operations ArrayList need to adjust the indexes according to
deletion or insetion if you are performing on middle indexes. Means,
an ArrayList having 10 elements, if you are inserting at index 5, then
you need to shift the indexes above 5 to one more.
The very best thing you can do for the whole world is to make the most of yourself.
-- Wallace Wattles
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