Greenfoot
Lecture 4. Greenfoot 1
Programming simulations and games in Java
Pablo Romero, Department of Informatics

Lecture plan
 Greenfoot in action
 The Wombats scenario
 Modifying the code
* Greenfoot Designed and implemented at the University of Kent and
Deakin University. Copyright held by Poul Henriksen and Michael
Koelling. Slides based on those by Eueung Mulyana
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Greenfoot
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Greenfoot
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Looking at the classes
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The Wombat class import necessary packages class header;
Wombat is a subclass from Actor data (constants and variables) class constructor and methods
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Constructor and leaf methods constructor  initialising direction and leavesEaten is there any Leaf object in my position?
this method is inherited from the superclass Actor remove that Leaf object update the variable leavesEaten
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The act method 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 the left!
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The turnLeft method change direction 90 degrees to the left
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The setDirection method this method is inherited from the superclass Actor
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The move method if object reaches one of the borders, do nothing!
the object moves forward; depends on its direction setLocation() is inherited from Actor
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The canMove method
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The canMove method these methods are inherited from Actor new coordinate if the object moves forward; depends on its direction
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The WombatWorld class
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Constructor populate randomLeaves
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The WombatWorld constructor calls the World constructor sets the background.
the method is inherited from the superclass World cell.jpg
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The populate method
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The randomLeaves method
Create a Leaf object at a random position (x,y); repeat howMany times
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So far
 Greenfoot environment to program simulations and games in java
 World and Actor are system classes
 The wombats program
 Leaf
 Wombat (getLeavesEaten, foundLeaf, eatLeaf, setDirection, turnLeft, canMove, move, act)
 WombatWorld (populate, randomLeaves)
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Exercise
 How would you change the behaviour of Wombat objects so that instead of always turning left, they could turn to other directions in a random way?
 GreenFoot. getRandomNumber(int limit)
Generates a random number between 0 and limit
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Exercise
 Create a new method, turnRandom(), that will turn to the left a random number of times. This method will replace the method turnLeft() in the act() method of Wombats. Use the method of the greenfoot library
GreenFoot. getRandomNumber(int limit) that produces a random integer between zero and limit-1.
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The method turnRandom
Generate a random number between 0 and 3 call turnLeft() turns times
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The updated method act
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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 !
Pablo Romero, Department of Informatics

Before and after
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to set the image of an object programmatically
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Before and after
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Adding Rocks class image for the Rock class
 New classes can be added easily
 Can import images for classes images available in the wombats scenario folder
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 However wombats can go through rocks
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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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Summary
 Greenfoot environment to program simulations and games (greenfoot.org)
 Provides an action loop
 World subclasses set up the world
 Actor subclasses define the characters of the game / simulation
 Sophisticated behaviour can be implemented in Java
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