Hello. I am a beginner in java, and a student in CS. Please help me with solve these questions so that I will be able to do it another time successfully by myself.

1.Please I need help drawing a class diagram for a student enrollment system that reflects the following specifications: The student enrollment system is composed of courses and people. Each course has a name, number of credits, and capacity. A student may enroll in the course, drop the course, or audit the course. There are two main groups involved in the Student Enrollment System: Student and Professor. There are two types of student: undergraduate and graduate. A professor may teach one or more classes. A student may be involved with zero or more classes, where involvement refers to enrolling, dropping, or auditing. A course may have zero or more pre-requisites.
Please, I'll like to implement the above UML class diagram in Java.

2. My other problem to solve is:

3. Following code is the Oval and FilledOval example. However, the Oval’s instance variables are public, which is not optimal. I want to change those instance variables to private and reimplement any code that depended on the public accessibility of those instance variables.
Please help me.
Thanks.

import java.awt.*;

public class Oval {
public int x, y, w, h;

public Oval(int x, int y, int w, int h) {
this.x = x; this.y = y; this.w = w; this.h = h;
}

public void draw(Graphics g) {
g.drawOval(x,y,w,h;
}

public int getWidth() { return w; }

public int getHeight() { return h; }

public Point getTopLeftPoint() { return new Point(x,y); }
//...other methods...
}

public class FilledOval extends Oval
{
public FilledOval(int x, int y, int w, int h)
{ super(x, y, w, h); }

public void draw(Graphics g)
{
g.fillOval(x, y, w, h);
}
}