Transcript Wombat help guide

Greenfoot
Game Programming Club
Keywords
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Class
Compile
Scenario
World
Actor
Execution Controls
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Methods
Parameters
Act
Run
int
Reference
• Resources: Greenfoot Tutorials located
on - missallgar-iteach.org>Gaming
Programming Project>Greenfoot
• You can download Greenfoot to your
personal computer from the Greenfoot
website. Java™ is a prerequisite for
Greenfoot.
What is Greenfoot?
Who developed it?
• “Greenfoot is a software tool designed to let
beginners get experience with object-oriented
programming.
• It supports development of graphical
applications in the Java™ Programming
Language.”
• “Greenfoot was designed and implemented at
the University of Kent, England, and Deakin
University, Melbourne, Australia.”
First Look
• Open Greenfoot from Start Menu
• If it doesn’t load with the Wombat scenario,
open it by selecting
Scenario/Open/Wombats.
• You should see something similar to what is
displayed as a background to this slide.
Screen Layout
• Large grid = “ the world
• Class display
– “World” and “Actor” classes part of
Greenfoot
– Other classes belong to the wombat
scenario.
• Execution Controls ( ‘Act’, ‘Run’, slider).
The [wombat] World Turns
• Place objects into the world
– Right click on the Wombat class, select ‘New
Wombat()’. Then place the new wombat in the
world. You have just created a wombat object and
placed it into the world.
– Use the same process to add several leaves
– Shortcut: Make sure the Leaf class is selected,
then hold down the Shift key and click into the
world several times.
The [wombat] World Turns
• Make objects act
– Click the ‘Act’ button in the execution controls.
Each object now acts – that is: each object does
whatever it wants to do.
• Run a scenario
– Click the ‘Run’ button. This is equivalent to clicking
the Act button over and over again, very quickly.
You will notice that the Run button changes to a
‘Pause’ button. Clicking it stops the whole show.
Invoke Single Methods
• Make sure you have a wombat in the
world, and the scenario is not running.
Then right-click on the wombat, and you
see that objects in the world also have a
pop-up menu (Figure 2).
– Try turnLeft().
– Try getLeavesEaten().
– Try act().
Invoking wombatWorld
Methods
• right-click the WombatWorld class and
select ‘new WombatWorld()’. What
happens? What type of function is
WombatWorld()? How did you know
that?
• Try populate().
• Try randomLeaves(int howMany).
Changing the Wombat Class
• Add the following method to the Wombat
class:
public void turnRandom()
{
// get a random number between 0 and 3...
int turns = Greenfoot.getRandomNumber(4);
// ...and turn left that many times.
for(int i=0; i<turns; i++) {
turnLeft();
}
}
Change act()
public void act()
{
if(foundLeaf()) {
eatLeaf();
}
else if(canMove()) {
move();
}
else {
turnLeft();
// change turnLeft() to turnRandom();
}
}
Compile
• Before you can execute your class
changes you must compile your project.
– Compile within the editor, or
– Compile from Greenfoot’s main window.
• Once you have successfully compiled,
you can create objects again.
– Compilation (if successful) automatically
instantiates a world object.
Changing Images
• 2 ways to change the image of objects
– You can change the image of a class, which will change the
default image for all objects of that class.
• Select ‘Set Image...’ from the class’s pop-up menu.
• Try this - change the leaf’s image to something else
– An object may change its image programmatically, which will
change only the individual object. Each object can change its
image as often as it likes.
• calling the ‘setImage’ method inherited from Actor.
– one version of setImage() expects a parameter of type
GreenfootImage
– one version of setImage() takes the name of a file (and then
reads that image file into a GreenfootImage and sets it).
Change to Left-facing Wombat
When the Wombat Moves Left
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Conveniently, the ‘wombats’ project contains
a file named ‘wombat-left.gif’ in its ‘images’
sub-folder.
To change the wombat image use the
following method call.
setImage("wombat-left.gif");
Edit the Wombat’s setDirection(int
Direction) method to display the correct
image when he is moving left.
Code
/*
if you want to use the left facing image for
upwards movement add
case NORTH :
setImage("wombat-left.gif");
setRotation(90);
break;
*/
case WEST :
setImage("wombat-left.gif");
setRotation(0);
break;
Documentation
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To make changes to object behavior, you
often need to make use of some standard
Greenfoot classes. Greenfoot provides four
important classes that you should know
about:
1.
2.
3.
4.
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World
Actor
GreenfootImage
Greenfoot.
Greenfoot’s online documentation:
http://www.greenfoot.org/doc/
Inspecting an Object
• Invoke the ‘Inspect’ function from the menu of
any wombat in the world.
• Populate the world and then inspect one of
the wombats. What do you see?
– some fields defined in the Wombat class (such as
‘leavesEaten’)
– some fields that are not defined in Wombat. The
additional fields (such as x, y and rotation) are
inherited from Actor and are present in all
Greenfoot objects.
• If a value is shown as an arrow symbol, then the field
contains a reference to another object, which can be
inspected in turn (by selecting and clicking ‘Inspect’).
Create a New Class
• Create a new actor class. Choose ‘New
subclass’ from the pop-up menu of Actor.
This will create a new class as a subclass of
Actor. When prompted for a class name, type
‘Rock’. You are also prompted to select an
image for the class.
• Select the image, click Ok, and a new class
named Rock is created.
• Open the editor for that class. Why don’t we
have to write code for the rock class?
Create a New Class
• Answer: Because rocks don’t act.
• Close the editor, compile and test (create an object) –
there are your rocks!
• Now populate the scenario a bit and test the
wombats. (You can use the world’s populate() and
randomLeaves() methods, and then add some
rocks by hand.)
• You will notice that you have rocks, but the wombats
still run through them. Can you modify the Wombat
class so that they don’t run through the rocks?
In Class Activity
• Add a Kangaroo class to the scenario. (In
case you weren’t taught kangaroo behavior, a
kangaroo will jump over at least one grid
square with each move but, like a Wombat,
will eat a leaf on the square on which she
lands.)
• Modify wombatWorld’s populate() to
initialize the world with 2 rocks, 1 kangaroo, 1
wombat and 7 leaves to the wombatWorld.
Final Request
• So that the wombat scenario reverts to
its original state, if you modified the
original, please reboot the computer.
• Thank you, and remember that Project
1 is due 11/10!