public class ArrayList implements List {
	private final static int INITIAL_CAPACITY = 20;

	private Object[] elements;
	private int numberOfElements;

	public ArrayList(int capacity){
		elements = new Object[capacity];
		numberOfElements = 0;
	}
	public ArrayList(){
		this(INITIAL_CAPACITY);
	}

	public int size(){
		return numberOfElements;
	}

	public Object get(int index){
		return elements[index];
	}

	public Object set(int index , Object element){
		elements[index] = element;
		return element;
	}

	public void add ( Object element){
		if ( size() >= elements.length)
			moreMemory(size()+1);
		elements[size()] = element;
		numberOfElements++;
	}

	private void moreMemory(int numElem){
		if (numElem> elements.length){
			Object[] aux = new Object[Math.max(numElem,2*elements.length)];
			System.arraycopy(elements,0,aux,0,elements.length);
			elements = aux;
		}
	}

	public void add(int index , Object element){
		if ( size() >= elements.length)
			moreMemory(size()+1);
		for ( int i = size() ; i> index; i--)
			elements[i] = elements[i-1];
		elements[index] = element;
		numberOfElements++;
	}

	public Object remove(int index){
		Object value = elements[index];
		for(int j= index; j<size()-1;j++)
			elements[j] = elements[j+1];
		numberOfElements--;
		return value;

	}
	@Override
	public Iterator<Object> iterator() {
		return new ArrayListIterator();
	}
	@Override
	public boolean contains(Object o) {
		checkElement(o);
		if (search(o) != -1)
			return true;
		return false;
	}
	@Override
	public boolean isEmpty() {
		return size() == 0;
	}
	@Override
	public Object remove(Object element) {
		checkElement(element);
		checkState();
		if (search(element) != -1)
		{
			return remove(search(element));
		}
		return null;
	}
	@Override
	public void clear() {
		Object[] aux = new Object[elements.length];
		elements = aux;

	}
	@Override
	public int indexOf(Object o) {
		checkElement(o);
		return search(o);
	}



	private void checkElement(Object element){
		if (element == null)
			throw new IllegalArgumentException("Error : el parametro es null");
	}

	private void checkState(){
		if (isEmpty())//lista vacia
			throw new IllegalStateException("Lista vacia");
	}

	private int search(Object element){
		int contador = 0;
		for (Object objeto:elements)
		{
			if (objeto.equals(element))
				return contador;
			else
				contador++;
		}
		return -1;
	}