First BlueJ Day Houston, 2006

1. First BlueJ DayHouston, 2006 David J. Barnes University of Kent

2. Getting started with BlueJ • My personal route to using BlueJ • Traditional approaches to teaching Java and OOP • The problems • How BlueJ addresses the problems First BlueJ Day, Houston, Texas, 1st March 2006

3. My personal route • Looking for an OO language • Blue at SIGCSE 1997 • Java by decree • Objects early via the command line. • Prentice-Hall textbook in 2000 First BlueJ Day, Houston, Texas, 1st March 2006

4. Traditional approaches to teaching Java • Strong influence of procedural programming • Heavy dependence on textbooks. • ‘Hello world’ • GUI-based First BlueJ Day, Houston, Texas, 1st March 2006

5. Hello World A necessary starting point? public class Hello { public static void main(String[] args){ System.out.println("Hello, world");} } First BlueJ Day, Houston, Texas, 1st March 2006

6. Text output public class OldMacDonald { public static void main(String[] args) { System.out.println("Old MacDonald had a farm"); System.out.println("E I E I O"); System.out.println("and on his farm he had a duck"); System.out.println("E I E I O"); System.out.println("With a quak quak here"); System.out.println("And a quak quak there"); System.out.println("Here a quak, there a quak"); System.out.println("Everywhere a quak quak"); System.out.println("Old MacDonald had a farm"); System.out.println("E I E I O"); } } First BlueJ Day, Houston, Texas, 1st March 2006

7. Text input and output import java.util.Scanner; public class Square { public static void main(String[] args) { Scanner reader = new Scanner(System.in); System.out.print("Input a number: "); int number = reader.nextInt(); System.out.println(number + " squared is " + (number * number)); } } First BlueJ Day, Houston, Texas, 1st March 2006

8. Classes to wrap functions Data Fields sqMeters Methods Conversion: square metres to square yards for a piece of fabric toSqYards readSqMeters displayFabric getDouble displayResult ... First BlueJ Day, Houston, Texas, 1st March 2006

9. GUIs import java.awt.*; public class Message extends Frame { Font f; public Message() { f = new Font("SansSerif", Font.BOLD, 24); setBackground(Color.yellow); setSize(400, 150); setVisible(true); } public void paint(Graphics g) { g.setFont(f); g.setColor(Color.blue); g.drawString("Welcome to Java", 100, 100); } } First BlueJ Day, Houston, Texas, 1st March 2006

10. GUIs (continued) public class FirstApp extends wheel.users.Frame { private wheels.users.Ellipse _ellipse; public FirstApp() { _ellipse = new wheels.users.Ellipse(); } // magic to let the FirstApp execute public static void main(String[] args) { FirstApp app = new FirstApp(); } } First BlueJ Day, Houston, Texas, 1st March 2006

11. The problems • Java’s main method is a requirement. • Traditional (procedural) curricula exert a strong influence. • GUI-based examples are attractive, but often carry a lot of baggage. First BlueJ Day, Houston, Texas, 1st March 2006

12. What I would like to teach • Classes and objects from day 1 • Object fundamentals • state • behaviour • multiplicity • independence • Let students experience objects • Emphasise modelling First BlueJ Day, Houston, Texas, 1st March 2006

13. Avoiding the problems • Jump start • Don't use main • Don't start with I/O • Beware the complexities of GUIs • custom libraries may have potential • Pick early examples very carefully • avoid simply converting old examples First BlueJ Day, Houston, Texas, 1st March 2006

14. What does BlueJ have to offer? • Liberation from a main method • A visual and interactive environment that is simple to use • An environment that supports OO concepts • the opportunity to experience objects • access to object state and behaviour First BlueJ Day, Houston, Texas, 1st March 2006

15. Using BlueJ – first steps Shapes and Pictures First BlueJ Day, Houston, Texas, 1st March 2006

16. Next steps • Avoid teaching BlueJ • BlueJ is a means to support OO teaching. • Choose examples that illustrate key concepts • Beware of falling back into old ways • Avoid the completeness trap First BlueJ Day, Houston, Texas, 1st March 2006

17. Next steps (continued) • Don't be afraid to use 'large' examples • Encourage students to read code • Apprenticeship is appropriate • Use sensible examples • Avoid giving them a blank screen • Design is hard • Syntax can be a stumbling block First BlueJ Day, Houston, Texas, 1st March 2006

18. Summary • Teaching proper OO may require a radical rethink of material • BlueJ provides excellent support for a truly OO curriculum • OO is possible from day 1 – ‘objects first’ First BlueJ Day, Houston, Texas, 1st March 2006