/**
 * A simplified of the interface java.util.Stack.
 * This interface contains fewer methods, the
 * method specifications are simplified and the
 * elements of the stack are strings.
 *
 * @author Franck van Breugel
 */
public interface Stack
{
    /**
     * Adds the given element to the top of this stack.
     *
     * @param element the element to be added to this stack.
     * @pre. element != null
     */
    void push(String element);

    /**
     * Removes the element from the top of this stack and
     * returns it.
     *
     * @pre. !isEmpty()
     * @return the element at the top of this stack.
     */
    String pop();

    /**
     * Tests whether this stack is empty.
     *
     * @return true if this stack is empty, false otherwise.
     */
    boolean isEmpty();
}