1. d.j.barnes@kent.ac.ukUniversity of Kent A practical introduction to Greenfoot www.greenfoot.org David Barnes Lecturer in Computer Science University of Kent

2. d.j.barnes@kent.ac.ukUniversity of Kent Overview Introducing object-orientation BlueJ The Greenfoot environment Greenfoot scenarios Practical application

3. d.j.barnes@kent.ac.ukUniversity of Kent Introducing object-orientation Building early understanding of key concepts is crucial: –Class –Object –State –Behaviour Hard to do without tool support – e.g. visualisation.

4. d.j.barnes@kent.ac.ukUniversity of Kent BlueJ IDE designed specifically for the teaching of introductory object- orientation. Developed by Michael Kölling. Good visualisation of key concepts. Interactivity brings these concepts to life. Typically used at u/g level.

5. d.j.barnes@kent.ac.ukUniversity of Kent Greenfoot An environment and framework that supports World+Actor scenarios. Developed by Michael, and Poul Henriksen. Provides visually engaging and concrete experiences for pre-University students. Built on top of BlueJ.

6. d.j.barnes@kent.ac.ukUniversity of Kent A few Greenfoot scenarios Wombats Ants Lifts Lunar lander

7. d.j.barnes@kent.ac.ukUniversity of Kent Practical application The framework API The crab world, by Michael Kölling. –Basic movement. –Actor interaction. –Simulation controls. –Key strokes. –Sound. –Image manipulation.

8. d.j.barnes@kent.ac.ukUniversity of Kent little-crab You will use the little-crab scenario in the crabworld folder. (Try to ignore the 2, 3, 4 and 5 folders which are cribs!) We start by using methods inherited from Animal to add movement, edge- detection and turning.

9. d.j.barnes@kent.ac.ukUniversity of Kent Worms Add a new subclass of Animal. No behaviour required. Add random turning to the Crab: –getRandomNumber in Greenfoot Add Worm detection to the Crab: –getOneObjectAtOffset in Actor –removeObject in World

10. d.j.barnes@kent.ac.ukUniversity of Kent Lobster Add Lobster as a subclass of Animal. –Copy Crab’s functionality. –Make it hunt crabs rather than worms. Stop the simulation when a crab is eaten: –stopSimulation in Greenfoot Variation: stop when the last crab is eaten.

11. d.j.barnes@kent.ac.ukUniversity of Kent Adding sound Play different sounds when crabs and worms are eaten (see the sounds folder): –playSound in Greenfoot Setup an initial population: –Use the constructor of CrabWorld. Change images as the crab moves: –setImage in Actor.

12. d.j.barnes@kent.ac.ukUniversity of Kent Other capabilities Detecting key presses: –isKeyDown in Greenfoot. Actor inspection. Interactive method invocation. Interactive movement: –setLocation in Actor. Linking actor interaction (plane scenario).

13. d.j.barnes@kent.ac.ukUniversity of Kent Review Greenfoot provides a rich environment and framework for scenario creation. Teachers can build scenarios that are attractive and interesting. An intermediate implementation layer provides an appropriate abstraction for target groups of students.