Understanding vectors

Question

I do not quite understand vectors regardless of how many pages I read on them, I have been assigned this program in my java class, I have written the following code so far, some of it was given to me, such as the v.add(cr) in the student class, however I have no clue as to what exactly is in my vector, where it is, and how to pull the variables that I need from it, which is what I ultimately need to do. If someone could please shed some light and point me in the right direction I would appreciate it. I have three classes, gradebook(supplies a gui with 3 buttons, one of which adds a student who has characteristics and up to 5 courses, one button which is supposed to print everything about the students(which is nowhere near done yet, don't worry about that), and one just to exit. Here's my code.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class Gradebook extends JFrame
private Button add;
private Button print;
private Button exit;
float[] gpa_array=new float[5];
private int num_students=0;
Student[] stu=new Student[5];
public Gradebook()
super("Student/Course GUI");
for(int a=0;a<5;a++)
stu[a]=new Student();
ButtonHandler handler = new ButtonHandler();
Container cat = getContentPane();
cat.setLayout(new FlowLayout());
add = new Button("Add Student");
add.addActionListener(handler);
cat.add(add);
print = new Button("Print");
print.addActionListener(handler);
cat.add(print);
exit = new Button("Exit");
exit.addActionListener(handler);
cat.add(exit);
setSize(800,600);
setVisible(true);
public class ButtonHandler implements ActionListener
public void actionPerformed(ActionEvent e)
if(e.getSource()== add)
num_students++;
stu[num_students].getData();
else
if(e.getSource() == print)
System.out.println("Printing all courses and students");
else
if(e.getSource() == exit)
System.exit(0);
public static void main(String[] args)
Gradebook app = new Gradebook();
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.Vector;
public class Student
private String name;
private String stringage;
private int age;
private float gpa;
private int num_courses;
private String stringnum_courses;
private int totalqp;
private Vector v = new Vector();
    public Student()
public void getData()
name = JOptionPane.showInputDialog(null,"Enter Student's Name","Enter Student's Name", JOptionPane.QUESTION_MESSAGE);
stringage = JOptionPane.showInputDialog(null,"Enter Student's Age","Enter Student's Age", JOptionPane.QUESTION_MESSAGE);
age = Integer.parseInt(stringage);
stringnum_courses = JOptionPane.showInputDialog(null,"Enter Number of Courses","Enter Number of Courses", JOptionPane.QUESTION_MESSAGE);
num_courses = Integer.parseInt(stringnum_courses);   
for(int a=0;a<num_courses;a++)
Course cr = new Course();
v.add(cr);
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class Course
    // instance variables - replace the example below with your own
    private int id;
    private String dept;
    private int credits;
    private String letter_grade;
    private String stringid;
    private String stringcredits;
    private int QP;
    public Course()
     getDept();
     getId();
     getCredits();
     getLettergrade();
     getQP();
    public void getDept()
       dept = JOptionPane.showInputDialog(null,"Enter Department","Enter Department", JOptionPane.QUESTION_MESSAGE);
public void getId()
stringid = JOptionPane.showInputDialog(null,"Enter Course ID","Enter Course ID", JOptionPane.QUESTION_MESSAGE);
id = Integer.parseInt(stringid);
public void getCredits()
stringcredits = JOptionPane.showInputDialog(null,"Enter Credits","Enter Credits", JOptionPane.QUESTION_MESSAGE);
credits = Integer.parseInt(stringcredits);
public void getLettergrade()
letter_grade = JOptionPane.showInputDialog(null,"Enter Letter Grade","Enter Letter Grade", JOptionPane.QUESTION_MESSAGE);
public void getQP()
if(letter_grade=="A")
QP=4*credits;
if(letter_grade=="B")
QP=3*credits;
if(letter_grade=="C")
QP=2*credits;
if(letter_grade=="D")
QP=credits;
if(letter_grade=="F")
QP=0;
}Here is the exact assignment just for any clarification purposes:
3 classes
Course
Student
Gradebook(main)
The Main class will have 3 Buttons to control the following Events:
1...Add student to system (initial data--name, gender, and course load (1 to
5 courses))
A Vector in the student class will be initially set to 5 courses for
each of 5 possible students
An array in the Gradebook class will hold references to each of the 5
student objects
2...Print all student data (along with gpa) High to low based upon gpa.
3...Exit

Answer 1

Hi could i solve your problem, how ever i understand you have a problem that what is stored in your vector and how to get from it... let me explain may you know it.
well
for(int a=0;a<5;a++)
stu[a]=new Student();
if(e.getSource()== add)
num_students++;
stu[num_students].getData(); ///specified student object
for(int a=0;a<num_courses;a++)
Course cr = new Course();
v.add(cr);
you are adding courses in the vector in the specified student object
well other method of vector could be vector.addElement();
'add' and 'addElement ' add an object type thing one after another....
so your ' v ' vector object will contain courses object when you will get them you need to do type cast for example you have to do same for print button what you have done for add button but only here you will getting things.
you will do below code in the student class by making new method ...
if( v != null && v.size > 0)
Courses objCourse = (Courses) v.elementAt(0);
you can get all courses object by looping them to the size of the vector
i hope this will work for what ever i understand your problem.
Cheers
ABId