And in the next step, we will add GameBall to each cell, for all nine of them.ĭouble click on the Board button to open the Board editor. For the cell marked as “0,2”, its column index is 0 and row index is 1.įor convenience, we will mark our cells as follow, cell_1, cell_2, cell_3, …, cell_9. Take the first cell (one marked “0,0” ) for example, its column index is 0 and row index index is also 0. Remember we make the background of the Board to be 3×3 cells of a cell size of 60 pixels? The index value of each cell is marked below. What good is a GameBall is it’s not on the board? So let’s put it on the board! But before doing that, let’s me take a minute to explain how the Board is laid out. We will add more to this class in Lesson 3.ĥ. This is all we will do with GameBall class for now. You should see the GameBall class under the Actor class as this. Right click on Actor button and select “ New subclass…” from the drop-down list.Īs shown in the image: enter GameBall as the class name, select steel-ball.png, and click OK to save. You should see the board now being drawn. Once the changes are saved, the changed status at the bottom would become saved.Ĭlick Compile all button at the bottom of main project window to recompile the program. Now hit Ctr+S or Class->Save to save the changes. The Board() function now should look like this: Second, add a line below the “super” call: First, change super(20,20,10) to super(3,3,60), because we want to create a world with 3×3 cells with a cell size of 60×60 pixels ( cell.jpg is 60×60 pixels). We need to make two changes to the Board() function. It is automatically called when a Greenfoot program starts and is what we will modify to create the background. The function Board() is the default constructor of the Board class. To edit it in Greenfoot’s class editor, double click the Board button and a window will pop up. If your Greenfoot is installed under C:/Greenfoot, then Board.java should be in C:/Greenfoot/scenarios/TicTacToe. The Board class is defined in Board.java which is located in /TicTacToe directory. Next, we will make it draw the background. Right click on the World button and click “New subclass”.Įnter “Board” as the class name and then select the cell image from backgrounds category. To create the TicTacToe board, we need to create a subclass of the World. Feel free to close the “wombat” scenario if you’d like. Select “Scenario”=>”New”, and then enter” TicTacToe” for the project name. For example, if your Greenfoot software is installed in C:/Greenfoot, then the sample scenarios will in under C:/Greenfoot/scenarios. There are several scenarios that came with the Greenfoot install and they are located in /scenarios. For example, if a class called Hybrid Car is a subclass of the class Car, then Hybrid Car will not only have the features of Car but also its own battery-related feature.Ī Greenfoot Scenario is just a project. Using the Lego theme, a subclass of a class Car has a “mold” similar to that of the Car class, but its “mold” is enhanced to include battery-related features. All objects of the Car type will have features like move, stop, etc. An object of the Car class can be said to be of the Car type. You can also consider a class like a type. If a class is named Car, then all objects of the Car class will have whatever features (aka functions) Car class has. A class is like a Lego mold and an object is like a Lego block. To compile a program is to convert the human-readable codes to machine-readable codes, which are binary codes.Ġ0000101010000001010101000110001010101010101010Ī function is a unit of execution. Usually they are written in human-readable format such as Java, C++, python, and Ruby, but sometimes they are written in more cryptic languages such as assembly language (bytes and registries, anyone?). Quick intro on Programs, Functions, Classes, Subclasses, and ObjectsĬomputer programs are one way for humans to communicate with machines.
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