(The Queue class) Section 10.6 gives a class for Stack. Design a class named Queue for storing integers. Like a stack, a queue holds elements. In a stack, the elements are retrieved in a last-in first-out fashion

/*********************************************************************************
* (The Queue class) Section 10.6 gives a class for Stack. Design a class named   *
* Queue for storing integers. Like a stack, a queue holds elements. In a stack,  *
* the elements are retrieved in a last-in first-out fashion. In a queue, the     *
* elements are retrieved in a first-in first-out fashion. The class contains:    *
*                                                                                *
* ■ An int[] data field named elements that stores the int values in the queue.  *
* ■ A data field named size that stores the number of elements in the queue.     *
* ■ A constructor that creates a Queue object with default capacity 8.           *
* ■ The method enqueue(int v) that adds v into the queue.                        *
* ■ The method dequeue() that removes and returns the element from the           *
*   queue.                                                                       *
* ■ The method empty() that returns true if the queue is empty.                  *
* ■ The method getSize() that returns the size of the queue.                     *
*                                                                                *
* Draw an UML diagram for the class. Implement the class with the initial array  *
* size set to 8. The array size will be doubled once the number of the elements  *
* exceeds the size. After an element is removed from the beginning of the array, *
* you need to shift all elements in the array one position the left. Write a     *
* test program that adds 20 numbers from 1 to 20 into the queue and removes      *
* these numbers and displays them.                                               *
*********************************************************************************/
public class Exercise_10_10 {
	/** Main method */
	public static void main(String[] args) {
		// Create a Queue object
		Queue queue = new Queue();

		// Adds 20 numbers from 1 to 20 into the queue
		for (int i = 1; i <= 20; i++) {
			queue.enqueue(i);
		}

		// Removes these numbers and displays them
		while (!queue.empty()) {
			System.out.print(queue.dequeue() + " ");
		}
		System.out.println();
	}
}

Queue.java

/*******************
*      Queue       *
*------------------*
* -elements: int[] *
* -size: int       *
* Queue()          *
* enqueue(v: int)  *
* dequeue(): int   *
* empty(): boolean *
* getSize(): int   *
*******************/

// Implement Queue class
public class Queue {
	// Data fields
	private int[] elements;
	private int size;
	public static final int DEFAULT_CAPACITY = 8;

	/** Construct a Queue object with default capacity */
	Queue() {
		elements = new int[DEFAULT_CAPACITY];
	}

	/** Adds v into the queue */
	public void enqueue(int v) {
		if (size >= elements.length) {
			int[] temp = new int[elements.length * 2];
			System.arraycopy(elements, 0, temp, 0, elements.length);
			elements = temp;
		}
		elements[size++] = v;
	}

	/** Removes and returs the element from the queue */
	public int dequeue() {
		int v = elements[0];
		int[] temp = new int[elements.length];
		System.arraycopy(elements, 1, temp, 0, size);
		elements = temp;
		size--;
		return v;
	}

	/** Return true if queue is empty */
	public boolean empty() {
		return size == 0;
	}

	/** Return size */
	public int getSize() {
		return size;
	}
}