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Posted 22 Dec 2011

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Sudoku game using Java

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5.00/5 (6 votes)
22 Dec 2011CPOL3 min read
Full description of constructing a game application in Java.


I wrote the original code for my Sudoku program using Visual Basic on Microsoft's Visual Studio IDE. This restricts the program to Windows. To allow the code to execute successfully on Windows and Linux, I decided to use the portability of the C++ language.

I documented this in a previous article: cross_platform.aspx.

My approach received much criticism as the “same code” could not be compiled directly into a platform application.

I abstracted the program to a series of functions which can be interfaced to the native GUI toolkits.

The GUI interface needs only some buttons, an image box, and mouse position. It is used only to call the functions in the core C++ program.


In Windows, I still use the Visual Basic IDE to provide the GUI. The functions are provided by compiling the C++ core to a managed assembly DLL.

In Linux, I use Glade to develop the GUI and associated code. The functions are added to the GUI code directly.

The image of the Sudoku uses an uncompressed bitmap file in Windows BMP file format. This can be displayed in Windows and Linux. It can also be directly worked on to produce the various images necessary for the program.

I still standby this method of generating cross-platform applications.

It is especially useful when we have:

  1. Most of the operational code able to be abstracted to a block of C++.
  2. Only a simple GUI is needed on the platform.

This does require individual compilation for each platform that it supports.

Another approach is to use code that can be directly run on any platform without special preparation. This could be software written in an interpreted language for which run-time packages are needed.

I have been learning Java so I decided to rewrite my Sudoku program and make it truly platform independent. Let's hope it will be “Write Once, Run Anywhere”, not “Write Once, Debug Everywhere”.

We can use Eclipse or the NetBeans IDE. Each has is own GUI toolkit. I do use Eclipse but I decided to use Java Foundation Classes (JFC) and Swing.

The code can be written and hacked with a text editor using javac to compile and java to run the application.

Game Code

The operational code needed to run the game is in:

public class Smethods
    public static byte select(byte[][] sudoku, byte number, byte position, byte step)
        if((sudoku[position*9 + number][step] == 0) || (sudoku[position*9 + number][step] > 9))
            return step;//end of number not possible or is selected

        step += 1; // we can select so write this step to the sudoku array
        int count = 0;
        for(count = 0; count < 729; count++)
            sudoku[count][step] = sudoku[count][step - 1]; //copy existing to next step
        for(count = 0; count < 9; count++)
            sudoku[position*9 + count][step] = 0; //Can't select any in box

        byte row =   (byte) (position/9);
        for(count = 0; count < 9; count++)
            sudoku[row * 81 + count * 9 + number][step] = 0; //horizontal row

        byte column =   (byte) (position%9);
        for(count = 0; count < 9; count++)
            sudoku[column * 9 + count * 81 + number][step] = 0;  //vertical row

        int brow =  (position/27)*243; //row block 0f 3
        column = (byte) (((position%9)/3)*27);  //Column block of 3
        byte incount;
        for(incount = 0; incount < 3; incount++)
            for(count = 0; count < 3; count++)
                sudoku[brow + column + count * 9 + incount * 81 + number ][step] = 0;  //box of 3 x 3
        }//end of 3 x 3 box
        //we have selected one number
        sudoku[position*9 + number][step] = (byte) (number + 11); //selected now 11 to 19
        return step;
    }//end of select a number
}//end of class

I have only shown one method in the Smethods class. We also have:

public static void start(byte[][] sudoku)
public static void trysudoku(byte[][] sudoku, byte startstep)

This provides all the calculations necessary to generate and solve Sudoku games.

Display Window

This is created by:

public class MySudoku 
 public static byte[][] sudoku = new byte[729][82];  //global array for sudoku solution
 public static byte step = 0; //global variable for solution step
 private static final int WindowWidth = 777; //its 777 pixels wide
 private static final int WindowHeight = 636; //its 636 pixels high 
 public static void ShowGUI() 
   Smethods.start(sudoku); //start array at step 0 has no numbers selected
   final byte border = 14;  //border for display
   JFrame f = new JFrame("MySudoku");
   BufferedImage image = null;
   try {
     image = File("sudoku.png"));
   } catch (IOException e) {
   }//end of try/catch
   f.setResizable(false);  //not to be resized
   f.setSize(WindowWidth, WindowHeight);  //size fixed by size of display and borders
   f.setLocation(0, 0); //start top left
   f.setLayout(new BorderLayout());  //north south east west and centre     
   f.add(new SPanel(new Dimension(WindowWidth,border)),  BorderLayout.NORTH);
   f.add(new SPanel(new Dimension(WindowWidth,border)),  BorderLayout.SOUTH);
   f.add(new SPanel(new Dimension(border,WindowHeight)),   BorderLayout.EAST);
   f.add(new SPanel(new Dimension(0,WindowHeight)),   BorderLayout.WEST);  //set the borders

    DisplayPanel dp =new  DisplayPanel();
    dp.setBackground(Color.BLACK);  //set the background of the sudoku display black
    f.add(dp, BorderLayout.CENTER);  //add the sudoku display panel
 }//end of show gui method
 public static void main(String[] args) {
   SwingUtilities.invokeLater(new Runnable() {
     public void run() {
   });  //end of run()
 }//end of main
}//end of MySudoku class

Display Panel

This is where all the hard work is done to create the GUI. It positions and monitors the push buttons.

It paints the Sudoku game display:

public class DisplayPanel extends JPanel implements ActionListener //create display panel
    private static final long serialVersionUID = 1L;
    private int DisplayWidth = 557; //sudoku display its 557 pixels wide
    private int DisplayHeight = 580; //sudoku display its 580 pixels high
    private int ButtonsWidth = 200; //button panel its 200 pixels wide
    private final Color LB = new Color(0xAD,0xD8, 0xE6);  //Light Blue 
    private final Color DB = new Color(0x1E,0x90, 0xFF);  //dodger blue
    private final Color P = new Color(0x80,0, 0x80);  //purple blank number 
    public DisplayPanel()   //construct the sudoku display panel
        addMouseListener(new MouseAdapter() //we listen for mouse clicks on this panel
            public void mousePressed(MouseEvent e) 
                selectNumber(e.getX(),e.getY());   //the called method on mouse click          
            }//end of mouse select
        });//end of mouse listener
        this.setLayout(new BorderLayout());
        JPanel pb = new JPanel();   //create the button panel
        pb.setPreferredSize(new Dimension(ButtonsWidth,DisplayHeight));
        FlowLayout FL = new FlowLayout();
        FL.setHgap(100);  //set the flow layout to give  symmetric display
        SButton EYS = new SButton("Enter Your Sudoku", "EYS");
        SButton SHS = new SButton("Start Hard Sudoku", "SHS");
        SButton SMS = new SButton("Start Medium Sudoku", "SMS");
        SButton SES = new SButton("Start Easy Sudoku", "SES");
        SButton GBS = new SButton("Go Back One Step", "GBS");
        SButton STS = new SButton("Solve This Sudoku", "STS");
        this.add(pb,BorderLayout.WEST); //add the push button panel to the display panel       
    }//end of constructor
}//end of my display panel class

The above only shows the constructor, we also have:

private void selectNumber(int x, int y)   //called method on mouse click
public Dimension getPreferredSize()  //set the preferred size of display panel
protected void paintComponent(Graphics g)  //called whenever the display panel needs painting
public void actionPerformed(ActionEvent e)  //call method for push button selected 

We also have two other classes used to create push buttons and panels.

class SButton extends JButton   //create a JButton with some fixed properties
public class SPanel extends Panel   //create border panels for the display

We then get the following window:



I have only been able to test it on Windows XP, Windows 7, and Vista. These machines had the correct Java runtime installed. If someone could spare the time, it would be nice to know if it works on Linux or Mac.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

carl morey
Australia Australia
I identify with the starfish.
I may be really stupid and have to use visual basic but at least I'm happy.

Comments and Discussions

Questionhow to run the code ? Pin
Member 1305924920-Apr-17 15:24
MemberMember 1305924920-Apr-17 15:24 
Questionreply Pin
Member 1089993523-Jun-14 20:06
MemberMember 1089993523-Jun-14 20:06 
QuestionAdditional Functionalities Pin
Member 1089993523-Jun-14 20:05
MemberMember 1089993523-Jun-14 20:05 
GeneralMy vote of 5 Pin
FazHel2-Mar-13 22:30
MemberFazHel2-Mar-13 22:30 
GeneralRe: My vote of 5 Pin
carl morey7-Mar-13 14:04
Membercarl morey7-Mar-13 14:04 

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