Greenfoot

1
Greenfoot

• November 8, 2009

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.

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.

4
First Look

• Open Greenfoot (found in the Applications folder)
• If it doesnt 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.

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).

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.

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.

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().

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).

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 i0 iltturns i)
• turnLeft()

11
Change act()

• public void act()
• if(foundLeaf())
• eatLeaf()
• else if(canMove())
• move()
• else
• turnLeft()
• // change turnLeft() to turnRandom()

12
Compile

• Before you can execute your class changes you
  must compile your project.
• Compile within the editor, or
• Compile from Greenfoots main window.
• Once you have successfully compiled, you can
  create objects again.
• Compilation (if successful) automatically
  instantiates a world object.

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 classs pop-up
  menu.
• Try this - change the leafs 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).

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 Wombats setDirection(int Direction)
  method to display the correct image when he is
  moving left.

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

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
• World
• Actor
• GreenfootImage
• Greenfoot.
• Greenfoots online documentation
  http//www.greenfoot.org/doc/

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).

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 dont we have
  to write code for the rock class?

19
Create a New Class

• Answer Because rocks dont 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 worlds 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 dont run through
  the rocks?

20
In Class Activity

• Add a Kangaroo class to the scenario. (In case
  you werent 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 wombatWorlds populate() to initialize the
  world with 2 rocks, 1 kangaroo, 1 wombat and 7
  leaves to the wombatWorld.

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!