/**
 * Implementation of a stack by means of an array.
 *
 * @author Franck van Breugel
 */
public class ArrayStack implements Stack
{
    private String[] content;
    private int size;
    //@ invariant this.content != null

    /**
     * Initializes this stack to be empty.
     */
    public ArrayStack()
    {
	this.size = 0;
	this.setContent(new String[1]);
    }

    /**
     * Returns the content of this stack.
     * 
     * @return the content of this stack.
     */
    private String[] getContent()
    {
	return this.content;
    }

    /**
     * Sets the content of this stack to the given content.
     * 
     * @param content the content of this stack.
     * @pre. pre. content ! null
     */
    private void setContent(String[] content)
    {
	this.content = content;
    }

    /**
     * Returns the size of this stack.
     * 
     * @return the size of this stack.
     */
    private int getSize()
    {
	return this.size;
    }

    /**
     * Sets the size of this stack to the given size.
     * 
     * @param size the size of this stack.
     */
    private void setSize(int size)
    {
	this.size = size;
    }

    public boolean isEmpty()
    {
	return this.getSize() == 0;
    }

    public String pop()
    {
	this.setSize(this.getSize() - 1);
	String top = this.getContent()[this.getSize()];
	this.getContent()[this.getSize()] = null;
	return top;
    }

    public void push(String element)
    {
	if (this.getContent().length == this.getSize())
	{
	    String[] temp = new String[this.getContent().length * 2];
	    for (int i = 0; i < this.getContent().length; i++)
	    {
		temp[i] = this.getContent()[i];
	    }
	    this.setContent(temp);
	}
	this.getContent()[this.getSize()] = element;
	this.setSize(this.getSize() + 1);
    }
}