import java.util.NoSuchElementException;

public class ArrayQueue implements Queue {
    final static int DEFAULT_SIZE= 16;
    private Object[] queue;
    private int front=0;
    private int rear=0;
    private int size;

    public ArrayQueue() {
        size= DEFAULT_SIZE;
        queue= new Object[size];
    }
    
    public void add(Object o) {
        int next = (rear+1) % size;
        if ( next == front)
            grow();
        rear = next;
        queue[rear] = o;
    }
    
    public Object remove() throws NoSuchElementException {
        if ( isEmpty() )
            throw new NoSuchElementException();
        else
        {
            front = (front+1) % size;
            return queue[front];
        }
    }
    
    public boolean isEmpty() {
        return (front == rear);
    }
    
    public void clear() {
        front= rear= 0;
    }
    
    private void grow() {
        Object[] old= queue;
        int oldSize= size;
        size *= 2;
        queue= new Object[size];
        if ( front < rear )
        {
            System.arraycopy(old, front, queue, front, rear - front + 1);
        }
        else if ( rear < front )
        {
            System.arraycopy(old, 0, queue, 0, rear + 1);
            System.arraycopy(old, front, queue, oldSize + front, oldSize - front);
        }
        // else if rear == front, no hay nada que copiar
    }
}