Introduction To
Greenfoot
Part-3
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Disclaimer
 This document is intended to give a beginner an introductory
material for the Greenfoot system. Greenfoot is a software
framework made by Poul Henriksen and Michael Koelling at
University of Kent / Deakin University. More information can be
found at http://www.greenfoot.org
 This document is available „AS IS“ free of charge for personal use
and non-commercial redistribution. It may not be sold for profit or
included in other packages which are sold for profit without written
authorisation. This document is distributed in the hope that it will
be useful, but WITHOUT ANY WARRANTY; your use of the
document is at your sole risk. Reusing and modifying (part of) this
document is allowed, as long as you state explicitly that your work is
based on the original document produced by the copyright holder:
Eueung Mulyana. The author can be contacted via
eueung-[at]-yahoo.com (http://kakihijau.googlepages.com).
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Purpose
 This is the second part of the document „Introduction to
Greenfoot“ and focuses on two topics: modification and
programming of the wombats scenario
 Part of the content of these slides is based on the
Greenfoot Tutorial made by Michael Koelling,
publicly accesible at the Greenfoot website,
http://www.greenfoot.org
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Outline
 Changing the Behaviour
 Changing Representations
 Creating New Classes
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Changing the Behaviour (1)
 We want to change the behaviour of Wombat objects :
instead of always turning left, they shall be able to turn to
other directions in a random way
 We will add an additional method, called turnRandom()
 Open the source code of the Wombat class, add the
following codes
Generate a random
number between 0 and 3
call turnLeft()
turns times
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Changing the Behaviour (2)
if you find leaves, eat !
if you don‘t find leaves, but you
can move forward, then move!
if you don‘t find leaves and you
also cannot move, then turn to a
random direction!
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Changing the Behaviour (3)
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Changing Representations (1)
 Visual representation (image) of an object can be
changed in two different ways
– Changing the „class image“; in this way, all objects of the same
class shall look the same (to the assigned class image)
– Changing the image programmatically; in this way, objects of the
same class might look different, depending on the
implementation
 These two ways might be combined!
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Changing Representations (2)
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Changing Representations (3)
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Changing Representations (4)
the result of populate() Additionally change the class image
after changin the class image then add 2 objects after modification
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Changing Representations (5)
to set the image of an object
programmatically
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Changing Representations (6)
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Creating New Classes (1)
 We could not only modify the class image for
the Rock class
behaviour of objects, but also add a
completely new type of objects i.e.
create new classes
 Right-click the class Actor and
choose item „New subclass ...“,
enter the class name and select a
class image in the dialog;
Greenfoot will automatically
generate your class !
 In this case we add a new class,
called Rock. The image for this images available in the wombats
class is already available in the scenario folder
wombats scenario folder
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Creating New Classes (2)
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Creating New Classes (3)
 To stop wombats
from walking
through rocks ...
check all Rock objects
in front of you;
if there is no Rock object,
return true (i.e. okay it‘s
clear!) , otherwise return
false (i.e. you cannot move!)
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Creating New Classes (4)
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