#27 - Implement Queue using Array in java - Data Structure series - Part -3

In this video , I have explained how to implement Queue using Array in java.

Array implementation of Queue is not dynamic in nature.
There are two most important operations of Queue:
enQueue: It is operation when we insert element into the queue.
deQueue: It is operation when we remove element from the queue.

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[triangularthoughts]

I have seen your dsa videos(logics) i crack the software development engineer -1 Thank you Naveen sir.

[VipinDahiya]

Thanks Naveen, for this awesome content, can we have this series continues,
i have implemented queue using Node class, feels good.
Kudos to you :)

[sandeepis]

Hi Naveen, logic was correct the catch was in enqueue method you should modify
if(rear == capacity){
rear = 0;
}
it solves the array full size issue and no need to increase your capacity

also in dequeue method modify
if (front == capacity){

+ " removed from the queue");
front = 0;
}
this will solve deleting first element twice.

I became your fan and hats off to your dedication and teaching :)

[sandipvishwakarma]

Got clear concept and logic. Thanks Naveen

[testinginsights-muktasharma]

Please come LIVE. 🙏
Looking forward to see you! Have many doubts to clear from.
Informative video🙏
Thank you!

[shadmairam]

what is the use of setting rear=0 if(rear==capacity-1); please explain.

[sravanthibana]

Hi Naveen, I guess the catch here is, both isEmpty() and isFull() methods are returning false because of which we dint see syso statements when the queue was full.

[ehkalanephaung]

It is a very cool tutorial, thank alot.

[sruthitenneti]

Still there is an issue in your code. You are not operating to the full capacity. U r operating only till capacity-1.try to insert values till the capacity without dequeue operation and then print the array everytime, then you will find the issue. To rectify the issue pls compare if(front==capacity) in enqueue and if(rear==capacity) in dequeue.

[DACSKishanKandu]

public class Queue{
int capacity;
int arr[];
int front;
int rear;
int size;

public Queue(int size){
this.size = size;
arr = new int[size];
front = 0;
rear = - 1;
capacity = 0;
}

public void enqueue(int element){
if(isFull()){
System.out.println("Queue is full, cannot enqueue anymore");
}else{
if(rear == size - 1){
rear = 0;
}else{
rear++;
}
arr[rear] = element;
capacity++;
System.out.println("Inserted element : " + element);
}
}

public int dequeue() {
if(isEmpty()){
System.out.println("Queue is empty, cannot dequeue element.");
return -1;
}else{
if(front == size - 1){
int returnEle = arr[front];
System.out.println("Dequeued element is : " + returnEle);
front = 0;
capacity--;
return returnEle;
}else{
int returnEle = arr[front];
System.out.println("Dequeued element is : " + returnEle);
front ++;
capacity--;
return returnEle;
}
}
}

public boolean isEmpty(){
return (capacity == 0);
}

public boolean isFull(){
return (capacity == size);
}

public static void main(String[] args){
Queue q1 = new Queue(5);





q1.enqueue(10);
q1.enqueue(20);
q1.dequeue();

q1.enqueue(30);
q1.enqueue(40);
q1.enqueue(50);
q1.enqueue(60);
q1.dequeue();
q1.dequeue();
q1.dequeue();
q1.dequeue();
q1.dequeue();
q1.dequeue();
q1.enqueue(30);
q1.enqueue(40);
q1.enqueue(50);
q1.enqueue(60);
q1.enqueue(30);
q1.enqueue(40);
q1.enqueue(50);
q1.enqueue(60);
q1.dequeue();

}


}

[sainathvallampatla]

Please explain the notations as well. Thanks for the teaching

[brandyplays]

naveen isnt ur enqueue wrong??see the step where( rear==capacity-1) u arent putting any data just directly making it as rear=0 ; shouldnt u write queuearr[rear]=data and then make rear=0 like how u have done for dequeue

[rahilkumar]

tried to iterate Queue using while loop and Iterator but it didn;'t worked. has anyone tried to iterate?

[josephcarcedo]

Hi sir, I think You forgot the method of Full Queue