Circular Arrays
August 26, 2016
Today’s exercise is to write a program that provides queues using a circular array. You should provide operations to make a new queue with a user-specified maximum size, determine if a queue is empty, add new elements to the end of the queue, and remove elements from the beginning of the queue.
Your task is to implement a queue as described above. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.
Programming Praxis 
A solution in Racket.
Here’s a solution in Java.
import java.util.NoSuchElementException; public class Queue<T> { private T[] array; private int start = 0; private int count = 0; @SuppressWarnings("unchecked") public Queue(int size) { array = (T[])new Object[size]; } public boolean add(T element) { if (count >= array.length) return false; array[(start+count) % array.length] = element; ++count; return true; } public T remove() { if (isEmpty()) throw new NoSuchElementException(); T element = array[start]; start = (start+1) % array.length; --count; return element; } public boolean isEmpty() { return count == 0; } public String toString() { StringBuffer sb = new StringBuffer("["); for (int i = 0; i < count; ++i) { if (i > 0) sb.append(", "); sb.append(array[(start + i) % array.length].toString()); } sb.append("]"); return sb.toString(); } public static void main(String[] args) { Queue<Integer> queue = new Queue<>(3); queue.add(1); System.out.println(queue); queue.add(2); System.out.println(queue); queue.add(3); System.out.println(queue); queue.add(4); // queue is full, so won't add. System.out.println(queue); queue.remove(); System.out.println(queue); queue.remove(); System.out.println(queue); queue.remove(); System.out.println(queue); try { queue.remove(); // queue is empty, so can't remove. } catch (NoSuchElementException e) {} queue.add(5); System.out.println(queue); } }Output: