Chapter 10 Exercise 10, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

10.10 (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 de queue() 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 Queue {

    private int[] elements;
    private int size;
    private int capacity;

    public Queue(int capacity) {
        this.capacity = capacity;
        elements = new int[capacity];
    }

    public Queue() {
        this(8);
    }

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

    }

    public int dequeue() {
        int v = elements[0];
        size--;
        for (int i = 0; i < size; i++) {
            elements[i] = elements[i + 1];
        }
        return v;
    }

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

    public int getSize() {
        return size;
    }

    public int getCapacity() {
        return capacity;
    }
}

public class Exercise_10 {

    public static void main(String[] args) {

        Queue queue = new Queue();
        // inserting 20 numbers into queue
        for (int i = 0; i < 20; i++) {
            queue.enqueue(i);
        }

        // displaying 20 numbers first in first out basis
        for (int i = 0; i < 20; i++) {
            System.out.printf("%2d ", queue.dequeue());
            if ((i + 1) % 5 == 0) System.out.printf("\n");
        }
    }


}