Simple Java Implementation of Queue

ArrayQueueJava.java

// www.abukhleif.com
class ArrayQueue {
  private final int[] queue;
  private int first = 0;
  private int last = 0;
  int size = 0;

  public ArrayQueue(int size) {
    queue = new int[size];
  }

  boolean isEmpty() { // check if the queue is empty!
    return size == 0;
  }

  boolean isFull() { // check if the queue is full!
    return size == queue.length;
  }

  boolean isExist(int x) { // check if a certain item is exist in the queue!
    for (int i = 0; i < size; i++) {
      if (queue[i] == x) {
        return true;
      }
    }
    return false;
  }

  public void addLast(int x) { // enqueue
    if (isFull()) {
      throw new RuntimeException("the queue is full");
    }
    queue[last] = x;
    size++;
    last = (last + 1) % queue.length;
  }

  public int removeFirst() { // dequeue
    if (isEmpty()) {
      throw new RuntimeException("the queue is empty");
    }
    int r = queue[first];
    first = (first + 1) % queue.length;
    size--;
    return r;
  }

  public int get(int index) { // get first item without removing it (peek)
    return queue[index];
  }
}