Question

I’m working on a program that makes a graphical model of Conway’s Game of Life, but it’s not letting me do anything once it’s launched; the buttons don’t work and the grid isn’t changing. What am I doing wrong?

import java.awt.*;
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;


public class gameOfLife extends JApplet{
    private static final long serialVersionUID = 1L;

cellClass cell;

public void init() {
    Container contentWindow = getContentPane();
    cell = new cellClass();{{
    setLayout(new FlowLayout()) }};
    contentWindow.add(cell);    
    }
} 

class grid extends JComponent{ 
    private static final long serialVersionUID = 2L;

    int XSIZE = 500;
    int YSIZE = 500;
    private int row;
    private int col;
    private int size = 5;
    private cellClass c;
    private Dimension preferredSize = new Dimension(XSIZE, YSIZE);

    public void paint(Graphics a) {
    int x, y;
        for(x=0; x<row; x++){
        for(y=0; y<col; y++){
            if(c.grid[x][y] != 0){
                a.drawRect(x * size, y * size, 5, 5);
            }
        }
    }
    a.drawRect(0, 0, XSIZE, YSIZE);

}

public grid(cellClass newGrid, int newRow, int newCol, int newSize) {
    setMinimumSize(preferredSize);
    setMaximumSize(preferredSize);
    setPreferredSize(preferredSize);
    this.row = newRow;
    this.col = newCol;
    this.size = newSize;
    this.c = newGrid;

}
}

class cellClass extends JPanel implements ActionListener{
private static final long serialVersionUID = 3L;

static final int ROW = 100;
static final int COL = 100;
static final int SIZE = 5;
static final int min = 2;
static final int max = 3;
static final int birth = 3;
public int genCount = 0;

public int[][] grid;
private int[][] nextGrid;

private GridBagLayout gridBag = new GridBagLayout();
private GridBagConstraints c = new GridBagConstraints();

JLabel title;
JLabel genCounter;
JButton oneGen;
JButton contPlay;
JButton stop;
public grid board;
public boolean paused = true;
public boolean canChange = true;

cellClass() {
    grid = new int [ROW][COL];
    nextGrid = new int[ROW][COL];

    makeGrid(grid);

    setLayout(gridBag);

    title = new JLabel("Game of Life Applet");
    c.gridx = 0;
    c.gridy = 0;
    c.gridwidth = 2;
    c.insets = new Insets(2,0,0,0);
    c.anchor = GridBagConstraints.WEST;
    add(title);

    board = new grid(this,ROW,COL,SIZE);
    c.gridx = 0;
    c.gridy = 2;
    c.gridwidth = 1;
    gridBag.setConstraints(board, c);
    add(board);

    oneGen = new JButton("Move one Generation");
    c.gridx = 0;
    c.gridy = 3;
    c.gridwidth = 1;
    gridBag.setConstraints(oneGen, c);
    add(oneGen);

    contPlay = new JButton("Play");
    c.gridx = 1;
    c.gridy = 3;
    c.gridwidth = 1;
            contPlay.setVisible(true);
    gridBag.setConstraints(contPlay, c);
    add(contPlay);

    stop = new JButton("Stop");
    c.gridx = 2;
    c.gridy = 3;
    c.gridwidth = 1;
            stop.setVisible(false);
    gridBag.setConstraints(stop, c);
    add(stop);

    genCounter = new JLabel("Generation: 0");
    c.gridx = 0;
    c.gridy = 1;
    c.gridwidth = 1;
    gridBag.setConstraints(genCounter, c);
    add(genCounter);
}

class ButtonListener {
    public void addActionListener(ActionEvent e) throws InterruptedException {
        JButton source = (JButton)e.getSource();

        if(source == oneGen){
            nextGen();
        }
        if(source == contPlay){
            paused = false;
            canChange = false;
                            contPlay.setVisible(false);
                            stop.setVisible(true);
            while (paused = false) {
                nextGen();
                Thread.sleep(1000);
            }
        }
        if(source == stop) {
            paused = true;
            canChange = false;
                            stop.setVisible(false);
                            contPlay.setVisible(true);
        }
    }
}

public void mouseClicked(MouseEvent e){
    int xco = e.getX() - board.getX();
    int yco = e.getY() - board.getY();
    if((e.getComponent() == board) && (paused == true)){
        if(grid[xco/5][yco/5] == 1){
            grid[xco/5][yco/5] = 0;
            board.repaint();
        }else if(grid[xco/5][yco/5] == 0){
            grid[xco/5][yco/5] = 1;
            board.repaint();
        }
    }
}

public void makeGrid(int[][] emptyGrid) {
    int x, y;
    for(x = 0; x < ROW; x++){
        for(y = 0; y < COL; y++){
            emptyGrid[x][y] = 0;
        }
    }
}

public void nextGen() {
    getNextGen();
    board.repaint();
    genCount++;
    genCounter.setText("Generation: " + Integer.toString(genCount));        
}

public void getNextGen() {
    int x, y, neighbor;
    makeGrid(nextGrid);
    for(x = 0; x < ROW; x++){
        for(y=0; y<COL; y++){
            neighbor = calculate(x,y);

            if(grid[x][y] != 0){
                if((neighbor >= min) && (neighbor <= max)) {
                    nextGrid[x][y] = neighbor;
                }
            }else {
                if(neighbor == birth){
                    nextGrid[x][y] = birth;
                }
            }
        }
    }
    makeGrid(grid);
    copyGrid(nextGrid,grid);
}

public void copyGrid(int[][] source, int[][] newGrid) {
    int x, y;
    for(x=0; x<ROW; x++){
        for(y=0; y<COL; y++){
            newGrid[x][y] = source[x][y];
        }
    }
}

private int calculate(int x, int y){
    int a, b, total;

    total = (grid[x][y]);
    for (a = -1; a<= 1; a++) {
        for (b = -1; b <= 1; b++){
            if(grid[(ROW + (x + a)) % ROW][(COL + (y + b)) % COL] != 0) {
                total++;
            }
        }
    }
    return total;
}

@Override
public void actionPerformed(ActionEvent arg0) {
    // TODO Auto-generated method stub

    }
}       

If anyone could tell me what’s wrong with it, that would be awesome.

Answer 1

One of your main problems is that you’re attempting to run a long process on the Swing event thread, also known as the Event Dispatch Thread or EDT, and this in effect will freeze your program. I see this problem occurring here:

class ButtonListener {
  public void addActionListener(ActionEvent e) throws InterruptedException {
     JButton source = (JButton) e.getSource();

     // ...

        while (paused = false) { // *******
           nextGen();
           Thread.sleep(1000);  // ******
        }
     }

     // ...

}

you have both a while(true) loop and a Thread.sleep(...) neither of which should be called on the event thread.

Instead you should be using a Swing Timer.

For more on the Swing event thread, please read Concurrency in Swing.

Also (1), where do you allow cells to be initialized to being alive? Without live cells to start with all generations will show nothing but an empty grid? Do you need to add a MouseListener to one or more of your components? I think that this would be a good idea.

Also (2) buttons generally work a lot better when you add ActionListeners to them as is well outlined in the Swing button tutorial. Have you gone through the Swing tutorials? If not, please check them out (find them here) as they will help you quite a bit, I think.

Also (3) you may be biting off more than you can chew in that you’re trying to solve too many problems at one time. When I create a GUI similar to this, I like to work on each portion of the program in isolation and get it working first before combining it all into one big program. So for instance, first work on the non-GUI model and get the generations working by running it through test code that calls the model’s methods. Next work on each portion of the GUI one at a time including the JButtons, then the MouseListener, then the display of the game of life, then implementing the generations.

It is much easier to debug smaller test programs then to try to debug the whole shebang, trust me.