package ArrayQueue;

//implement generics using type T <T>

public class ArrayQueue<T> implements InterfaceQueue<T> {

private T[] items; //we need array of objects

private int queueCount; //this will show number of elements currently in the queue

public int maxSize; //this will show max size of elements that fit on queue

/*

*@overloaded constructor to allow the queue collection to be initialised

*

*@param maxSize number of elements the queue will be able to hold

*/

public ArrayQueue (int maxSize) {

//if there are 3 member variables (see above),

//there is a good chance you will also need 3

//sets of things in the constructor method

this.maxSize = maxSize;

items = (T[]) new Object[this.maxSize];//instantiate space of maxSize for the items array and typecast

this.queueCount = 0;

}

public int size() {

return queueCount;

}

public boolean isEmpty() {

if (queueCount == 0 ) return true;

else return false;

}

public void enqueue(T element) {

//have to check if element is null

if(element == null) {

throw new NullPointerException("Null element passed to enqueue");

}

//have to check if queue is full

if (queueCount >= maxSize) {

throw new IndexOutOfBoundsException("Queue's full");

}

//can add onto queue

//1. add element at position in the array indicated by queueCount

items[queueCount] = element;

//increment it

queueCount++;

}

public T dequeue() {

//check for these error conditions:

//check if queue is empty

if (queueCount == 0) {

//TO DO index out of bounds is not exactly the right exception below

//throw new IndexOutOfBoundsException("queue is empty");

//so let's use something differen that uses the emptyQueueException.java class

throw new EmptyQueueException("queue is empty");

}

//steps

//1. create a temporary variable to hold the element at the front of the queue

//2. queue requires first item on the queue to be the first off the queue.

//this means we'll always dequeue from index == 0 in the array

//element = items at index position 0

T element = items[0];

//we must shift each element in the array one place to the left. let's use a for loop

for(int index = 0; index < queueCount; index++) {

items[index] = items[index+1];

}

//4.let's decrement the count

queueCount--;

return element;

}

public T peek() {

//check for errors

if(queueCount == 0 ) {

throw new EmptyQueueException("Queue is empty");

}

//create temp variable to hold the element at front of queue

//

return items[0];

}

public String toString() {

String str = "FRONT[";

for(int index = 0; index < queueCount; index++) {

str += " " + items[index];

}

return str += "]BACK";

}

}