Implement a queue data structure in Java that can enqueue and dequeue elements. The queue should have a maximum size of n and should be implemented using an array. The enqueue operation should add elements to the back of the queue, and the dequeue operation should remove elements from the front of the queue. If the queue is full, the enqueue operation should throw an exception, and if the queue is empty, the dequeue operation should return null. The queue should also have a method to check if it is empty and a method to get the size of the queue. Finally, the implementation should use generics to allow storing of any data type in the queue.
Implement a queue data structure in Java that can enqueue and dequeue elements. The queue should have a maximum size of n and should be implemented using an array. The enqueue operation should add elements to the back of the queue, and the dequeue operation should remove elements from the front of the queue. If the queue is full, the enqueue operation should throw an exception, and if the queue is empty, the dequeue operation should return null. The queue should also have a method to check if it is empty and a method to get the size of the queue. Finally, the implementation should use generics to allow storing of any data type in the queue.
user
Here's an implementation of a queue data structure in Java using an array:

```
public class Queue<T> {

    private int maxSize;
    private int front;
    private int rear;
    private int currentSize;
    private T[] queue;

    @SuppressWarnings("unchecked")
    public Queue(int size) {
        this.maxSize = size;
        this.front = 0;
        this.rear = -1;
        this.currentSize = 0;
        this.queue = (T[]) new Object[size];
    }

    public void enqueue(T item) throws QueueFullException {
        if (isFull()) {
            throw new QueueFullException("Queue is full");
        }
        rear = (rear + 1) % maxSize;
        queue[rear] = item;
        currentSize++;
    }

    public T dequeue() {
        if (isEmpty()) {
            return null;
        }
        T item = queue[front];
        front = (front + 1) % maxSize;
        currentSize--;
        return item;
    }

    public int size() {
        return currentSize;
    }

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

    public boolean isFull() {
        return currentSize == maxSize;
    }
}
```

Explanation:

- `maxSize`: maximum size of the queue
- `front`: index of the first element in the queue
- `rear`: index of the last element in the queue
- `currentSize`: current number of elements in the queue
- `queue`: array to hold the elements in the queue

In the constructor, we initialize the variables with their initial values. We also create the array using the `maxSize` parameter passed to the constructor, casting it to type `T[]`.

In the `enqueue` method, we check if the queue is full using the `isFull` method. If it is full, we throw a `QueueFullException`. If it is not full, we increment `rear` to point to the next position in the queue (taking into consideration the wrapping around when `rear` reaches the end of the array), and then add the item to the queue. We also increment `currentSize`.

In the `dequeue` method, we check if the queue is empty using the `isEmpty` method. If it is empty, we return null. If it is not empty, we retrieve the item at the front of the queue, increment `front` to point to the next position in the queue (again taking into consideration wrapping around), decrement `currentSize`, and then return the item.

The `size`, `isEmpty`, and `isFull` methods are self-explanatory. They simply return the current number of elements in the queue, whether the queue is empty, and whether the queue is full, respectively.
assistant
Can you please explain a bit more about the `%` operator used in the `enqueue` and `dequeue` methods?
user
Sure! The `%` operator, also known as the modulus or remainder operator, returns the remainder of the division operation. In this queue implementation, we use `%` to wrap around the queue array when `front` or `rear` reaches the end of the array. For example, let's say we have a queue with a maximum size of 5, and the `rear` is currently at index 4 (the last index of the array). If we try to enqueue an item, we need to move `rear` to the next index, which is 0 since the array is circular. We can calculate the next index using the expression `(rear + 1) % maxSize`. So, `(4 + 1) % 5` gives us 0, which is the correct index to enqueue the item. If we keep enqueuing items, the `rear` index will keep incrementing until it reaches 4 again, then it will wrap around to 0. We use the same approach for wrapping around the front index when dequeuing items from the queue. I hope that helps!
assistant