public class DynamicQueue {

private int rear , front , size;

private static int CAPACITY = 16;

private int[] queueRep;

//empty constructor intialization process

public DynamicQueue(){

rear = 0 ; front = 0 ; size = 0;

queueRep = new int[CAPACITY];

}

//parameterize constructor

public DynamicQueue(int cap) throws NullPointerException{

if(cap <= 0){

throw new NullPointerException("please give a valid capacity for a queue");

}

CAPACITY = cap;

queueRep = new int[cap];

}

public int size(){

return size;

}

public boolean isEmpty(){

return (size == 0);

}

public int front(){

return queueRep[front];

}

public void enqueue(int data)throws NullPointerException , IllegalStateException{

if(size == CAPACITY){

// System.out.println("Size and capacity are equal");

expand();

}

// System.out.println("Size and capacity not equal" + rear);

size++;

queueRep[rear] = data;

rear = (rear + 1) % CAPACITY;

}

public int dequeue(){

int data = queueRep[front];

size--;

queueRep[front] = Integer.MIN_VALUE;

front = (front+1)% CAPACITY;

return data;

}

public void expand(){

int length = size;

int newQueue[] = new int[length<<1];

System.out.println("rear at : " + rear + " front at : " + front);

// if front and rear pointer are pointing at the exact same location

if(rear == 0){

for(int i = 0 ; i < queueRep.length ; i++){

newQueue[i] = queueRep[i];

}

}

else{

int j = 0, temp = front;

//System.out.println("temp value : " + temp + " and rear " + rear);

//we go only till one element before rear pointer , because there might be a issue of rear and front both pointer pointing at same location other than 0

while(temp != rear - 1){

newQueue[j] = queueRep[temp%CAPACITY];

j++;

temp = (temp+1) % CAPACITY;

}

newQueue[j] = queueRep[temp];

}

//resetting rear , size , capacity , queueRep and front

queueRep = newQueue;

front = 0;

rear = size;

CAPACITY *= 2;

}

public String toString(){

String result = "[";

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

result += Integer.toString(queueRep[(front + i) %CAPACITY]);

if(i < size - 1) result += ", ";

}

result += "]";

return result;

}

public static void main(String args[]) {

DynamicQueue dq = new DynamicQueue(5);

dq.enqueue(1);System.out.println(dq.toString());

dq.enqueue(2);System.out.println(dq.toString());

dq.enqueue(3);System.out.println(dq.toString());

dq.enqueue(4);System.out.println(dq.toString());

dq.enqueue(5);System.out.println(dq.toString());

System.out.println("removed element : "+dq.dequeue());

System.out.println(dq.toString());

dq.enqueue(6);System.out.println(dq.toString());

dq.enqueue(7);System.out.println(dq.toString());

dq.enqueue(8);System.out.println(dq.toString());

dq.enqueue(9);System.out.println(dq.toString());

dq.enqueue(10);

System.out.println(dq.toString());

dq.enqueue(11);

System.out.println("removed element : "+dq.dequeue());

System.out.println(dq.toString());

System.out.println("removed element : "+dq.dequeue());

System.out.println(dq.toString());

System.out.println("removed element : "+dq.dequeue());

System.out.println(dq.toString());

System.out.println("removed element : "+dq.dequeue());

System.out.println(dq.toString());

}

}