package studentDB;
/**
 *	Maintains a list of courses.  Courses may be entered
 *	into the list and retrieved from the list.
 */
public class CourseListImpl extends ListImpl implements CourseList {
    /**
     *	Returns the course at position n.  Indexing is
     *  zero-based, so it must hold that 0<=n<numElements.
     */
    public Course get (int n) {
	return (Course) getElement (n);
    }

    /**
     *	Returns the first course in the list.  The list may not
     *  be empty.
     *	@return The first course in the list.
     */
    public Course first() {
	return (Course)firstElement();
    }
    
    /**
     *  Returns the list of courses following the first course.
     *	The list may not be empty.
     *	@return The list of courses following the first course.
     */
    public CourseList rest() {
	return (CourseList)restElements();
    }


    /**
     *	Adds the given course to the end of the list.
     *	If the course is already in the list, has no effect.
     *	@param newCourse The course being added
     */
    public void add (Course newCourse) {
	// If the course is already in the list, has no effect.
	// Otherwise, add the course to the rest of the list.
	if (!inList(newCourse)) {
	    addElement (newCourse, new CourseListImpl());
	}
    }

    /**
     *  Returns a printable version of the list of courses.
     */
    public String toString () {
	if (isEmpty()) {
	    return null;
	} else {
	    String r = first().getTitle();
	    for (int i=1; i<numElements(); i++) {
		r = r + " " + get (i).getTitle();
	    }
	    return r;
	}
    }
}