Queue implementation in java

If you want to practice data structure and algorithm programs, you can go through 100+ java coding interview questions.

In this post , we will see how to implement Queue using Array in java.
Queue is abstract data type which demonstrates First in first out (FIFO) behavior. We will implement same behavior using Array.

Although java provides implementation for all abstract data types such as Stack, Queue and LinkedList but it is always good idea to understand basic data structures and implement them yourself.

Please note that 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.

Java Program to implement Queue using Array:

package org.arpit.java2blog;

public class QueueUsingArrayMain {

    private int capacity;
    int queueArr[];
    int front;
    int rear;
    int currentSize = 0;

    public QueueUsingArrayMain(int sizeOfQueue) {
        this.capacity = sizeOfQueue;
        front = 0;
        rear = -1;
        queueArr = new int[this.capacity];
    }

    /**
     * this method is used to add element in the queue
     * 
     * @param data
     */
    public void enqueue(int data) {
        if (isFull()) {
            System.out.println("Queue is full!! Can not add more elements");
        } else {
            rear++;
            if (rear == capacity - 1) {
                rear = 0;
            }
            queueArr[rear] = data;
            currentSize++;
            System.out.println(data + " added to the queue");
        }
    }

    /**
     * This method removes an element from the front of the queue
     */
    public void dequeue() {
        if (isEmpty()) {
            System.out.println("Queue is empty!! Can not dequeue element");
        } else {
            front++;
            if (front == capacity - 1) {
                System.out.println(queueArr[front - 1] + " removed from the queue");
                front = 0;
            } else {
                System.out.println(queueArr[front - 1] + " removed from the queue");
            }
            currentSize--;
        }
    }

    /**
     * This method is use to check if element is full or not
     * 
     * @return boolean
     */
    public boolean isFull() {
        if (currentSize == capacity) {
            return true;
        }
        return false;
    }

    /**
     * This method is use to check if element is empty or not
     * 
     * @return
     */
    public boolean isEmpty() {

        if (currentSize == 0) {
            return true;
        }
        return false;
    }

    public static void main(String a[]) {

        QueueUsingArrayMain queue = new QueueUsingArrayMain(5);
        queue.enqueue(6);
        queue.dequeue();
        queue.enqueue(3);
        queue.enqueue(99);
        queue.enqueue(56);
        queue.dequeue();
        queue.enqueue(43);
        queue.dequeue();
        queue.enqueue(89);
        queue.enqueue(77);
        queue.dequeue();
        queue.enqueue(32);
        queue.enqueue(232);
    }
}

package org.arpit.java2blog;

public class QueueUsingArrayMain {

private int capacity;

int queueArr[];

int front;

int rear;

int currentSize = 0;

public QueueUsingArrayMain(int sizeOfQueue) {

this.capacity = sizeOfQueue;

front = 0;

rear = -1;

queueArr = new int[this.capacity];

}

/**

* this method is used to add element in the queue

* @param data

public void enqueue(int data) {

if (isFull()) {

System.out.println("Queue is full!! Can not add more elements");

} else {

rear++;

if (rear == capacity - 1) {

rear = 0;

}

queueArr[rear] = data;

currentSize++;

System.out.println(data + " added to the queue");

}

/**

* This method removes an element from the front of the queue

public void dequeue() {

if (isEmpty()) {

System.out.println("Queue is empty!! Can not dequeue element");

} else {

front++;

if (front == capacity - 1) {

System.out.println(queueArr[front - 1] + " removed from the queue");

front = 0;

} else {

System.out.println(queueArr[front - 1] + " removed from the queue");

}

currentSize--;

}

/**

* This method is use to check if element is full or not

* @return boolean

public boolean isFull() {

if (currentSize == capacity) {

return true;

}

return false;

}

/**

* This method is use to check if element is empty or not

* @return

public boolean isEmpty() {

if (currentSize == 0) {

return true;

}

return false;

}

public static void main(String a[]) {

QueueUsingArrayMain queue = new QueueUsingArrayMain(5);

queue.enqueue(6);

queue.dequeue();

queue.enqueue(3);

queue.enqueue(99);

queue.enqueue(56);

queue.dequeue();

queue.enqueue(43);

queue.dequeue();

queue.enqueue(89);

queue.enqueue(77);

queue.dequeue();

queue.enqueue(32);

queue.enqueue(232);

}

When you run above program, you will get below output:

6 added to the queue
6 removed from the queue
3 added to the queue
99 added to the queue
56 added to the queue
3 removed from the queue
43 added to the queue
99 removed from the queue
89 added to the queue
77 added to the queue
56 removed from the queue
32 added to the queue
232 added to the queue

That’s all about Queue implementation in java.

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Queue implementation in java

Java Program to implement Queue using Array:

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