Slide #1.

Greenfoot November 8, 2009
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Slide #2.

Reference • Open the Greenfoot Tutorial located on the lab computers at Applications/Greenfoot 1.5.1/tutorial/tutorial.html • You can download Greenfoot to your personal computer from the Greenfoot website. Java™ is a prerequisite for Greenfoot.
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Slide #3.

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.”
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Slide #4.

First Look • Open Greenfoot (found in the Applications folder) • 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.
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Slide #5.

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).
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Slide #6.

The [wombat] World Turns • Place objects into the world – Control-click the Wombat class, select ‘New Wombat()’. Then click anywhere 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.
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Slide #7.

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.
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Slide #8.

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().
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Slide #9.

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).
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Slide #10.

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
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Slide #11.

Change act() public void act() { if(foundLeaf()) { eatLeaf(); } else if(canMove()) { move(); } else { turnLeft(); // change turnLeft() to turnRandom(); } }
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Slide #12.

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.
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Slide #13.

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).
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Slide #14.

Change to Left-facing Wombat When the Wombat Moves Left • • • 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.
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Slide #15.

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;
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Slide #16.

Documentation • 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. • World Actor GreenfootImage Greenfoot. Greenfoot’s online documentation: http://www. greenfoot.org/doc/
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Slide #17.

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’).
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Slide #18.

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?
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Slide #19.

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?
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Slide #20.

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.
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Slide #21.

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!
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