import java.util.Vector;

/**
 * IStack implementation using a Java Vector to hold its elements.
 * @author Jeff Raab
 */
public class VectorStackSolution implements IStack {

    /** Vector used to hold the elements on this. */
    protected Vector elements = new Vector();
    
    /** Constructs a new Java stack. */
    public VectorStackSolution() {}
    
    /** 
     * Pushes the given object onto this.
     * @param anObject object to push
     */
    public void push(Object anObject) {
        elements.add(anObject);
    }
    
    /** Removes and returns the top object on this. */
    public Object pop() {
        if (isEmpty()) {
            throw new RuntimeException("Stack is empty");
        }

        return elements.remove(size() - 1);
    }
    
    /** Returns the top object on this. */
    public Object top() {
        if (isEmpty()) {
            throw new RuntimeException("Stack is empty");
        }

        return elements.elementAt(size() - 1);
    }
    
    /** Returns the number of objects on this. */
    public int size() {
        return elements.size();
    }
    
    /** Returns whether or not this is empty. */
    public boolean isEmpty() {
        return elements.isEmpty();
    }
}