在方法中初始化后如何正确显示JFrame

Question

This is a long question, so bear with me for a minute. I'm making a Game of Life application which first shows a JFrame with a grid of JButtons. If you click on a JButton its background turns black and when activated again, its background turns back to white. My code:

public class Choose implements ActionListener {
public final static int DIMENSION = 50;
Color BLACK = new Color(0,0,0);
Color WHITE = new Color(255,255,255);
JFrame choose;
JButton[] choice;
JButton clear, fill, go;
JPanel baseChoose, baseFrame, buttonsAndText;
GridLayout base;

public Choose() {
    choose = new JFrame("Make your own game");
    choice = new JButton[DIMENSION*DIMENSION];

    baseChoose = new JPanel();
        baseChoose.setSize(500, 500);
    buttonsAndText = new JPanel();

    buttonsAndText.add(clear = new JButton("Clear"));
        clear.addActionListener(this);
    buttonsAndText.add(fill = new JButton("Fill"));
        fill.addActionListener(this);
    buttonsAndText.add(go = new JButton("Go"));
        go.addActionListener(this);

    base = new GridLayout(DIMENSION, DIMENSION);
        base.setHgap(-1);
        base.setVgap(-1);

    baseChoose.setLayout(base);
    choose.add(baseChoose);
    choose.add(buttonsAndText);

    JLabel text = new JLabel("Press 'Go' to start.");
    buttonsAndText.add(text);

    for (int i = 0; i < (DIMENSION*DIMENSION); i++) {
        baseChoose.add(choice[i] = new JButton());
        choice[i].setBackground(WHITE);
        choice[i].addActionListener(this);
    }

    choose.setSize(500, 800);
    choose.setVisible(true);
    choose.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    choose.setResizable(false);
}

public void actionPerformed(ActionEvent e) {
    JButton b = (JButton)e.getSource();

    for (int i = 0; i < (DIMENSION*DIMENSION); i++) {
        if (b == choice[i]) {
            if (b.getBackground() == BLACK) {
                choice[i].setBackground(WHITE);
            } else if (b.getBackground() == WHITE) {
                choice[i].setBackground(BLACK);
            }
        }
    }

    if (b == clear) {
        for (int i = 0; i < (DIMENSION*DIMENSION); i++) {
            choice[i].setBackground(WHITE);
        }
        choose.validate();
        choose.repaint();
    }

    if (b == fill) {
        for (int i = 0; i < (DIMENSION*DIMENSION); i++) {
            choice[i].setBackground(BLACK);
        }
        choose.validate();
        choose.repaint();
    }

    if (b == go) {
        int states[] = new int[DIMENSION*DIMENSION];
        for (int i = 0; i < DIMENSION*DIMENSION; i++) {
            System.out.println(choice[i].getBackground() == BLACK);
            if (choice[i].getBackground() == BLACK) {
                states[i] = 1;
            } else if (choice[i].getBackground() == WHITE) {
                states[i] = 0;
            }
        }
        choose.dispose();
        Gui own = new Gui(states);
    }
}
}

In the main method I make an instance of this class, when you have chosen your buttons to activate, you can click the go button to actually show the Game of Life.

public class Gui  {
public final static int DIMENSION = 50;
Color BLACK = new Color(0,0,0);
Color WHITE = new Color(255,255,255);
JFrame frame, ownFrame;
JPanel baseFrame;
GridLayout base;

public Gui(int[] states) {
    frame = new JFrame("Game of Life by Boris Verwoerd");

    baseFrame = new JPanel();
        baseFrame.setSize(500, 500);

    frame.add(baseFrame);

    base = new GridLayout(DIMENSION, DIMENSION);
        base.setHgap(-1);
        base.setVgap(-1);

    baseFrame.setLayout(base);

    JPanel[] box = new JPanel[DIMENSION*DIMENSION];

    for (int i = 0; i < (DIMENSION*DIMENSION); i++) {
        baseFrame.add(box[i] = new JPanel());
        box[i].setBorder(BorderFactory.createLineBorder(Color.black));
    }

    frame.setSize(500, 500);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setResizable(false);
    frame.validate();
    frame.repaint();

    gameLoop(box, frame, states);
}

private static void gameLoop(JPanel[] boxes, JFrame theFrame, int[] states) {
    int[] newstates = new int[DIMENSION*DIMENSION];
    for (int i = 0; i < 20; i++) {

        newstates = Maths.render(boxes, theFrame, states);
        states = newstates;
        theFrame.validate();
        theFrame.repaint();

        try {
            Thread.sleep(100);                 //1000 milliseconds is one second.
        } catch(InterruptedException ex) {
            Thread.currentThread().interrupt();
        }
    }
}

public static int getDim() {
    return DIMENSION;
}

}

When pressing go, a new JFrame launches but the screen is totally white, only after the gameLoop has ended it shows the JPanel grid.

Only when I make an instance of Gui from the main method with an all zero array states it shows it correctly. I've tried so many things to come up with a solution but I can't understand why it causes this white screen instead of the Grid. Hence my question is: How can I show my instance of Gui correctly, without the white screen when initialized from a method?

• Sorry for the long post/code!

Edit:

This is my Maths class:

public class Maths {
static Color BLACK = new Color(0,0,0);
static Color WHITE = new Color(255,255,255);

public static int[] render(JPanel[] box, JFrame frame, int[] state) {
    int[] newstates = new int[Gui.getDim()*Gui.getDim()];
    for (int i = 0; i < (Gui.getDim()*Gui.getDim()); i++) newstates[i] = 0;

    for (int i = (Gui.getDim()+1); i < (Gui.getDim()*Gui.getDim() - (Gui.getDim()+1)); i++) {
        if (state[i] == 1) {
            int aliveNeighbours = 0;
            if (state[i-(Gui.getDim()+1)] == 1) aliveNeighbours++;
            if (state[i-Gui.getDim()] == 1) aliveNeighbours++;
            if (state[i-(Gui.getDim()-1)] == 1) aliveNeighbours++;
            if (state[i-1] == 1) aliveNeighbours++;
            if (state[i+1] == 1) aliveNeighbours++;
            if (state[i+(Gui.getDim()-1)] == 1) aliveNeighbours++;
            if (state[i+Gui.getDim()] == 1) aliveNeighbours++;
            if (state[i+(Gui.getDim()+1)] == 1) aliveNeighbours++;

            if (aliveNeighbours == 2 || aliveNeighbours == 3) {
                box[i].setBackground(BLACK);
                newstates[i] = 1;
            } else {
                box[i].setBackground(WHITE);
                newstates[i] = 0;
            }

        } else if (state[i] == 0) {
            int aliveNeighbours = 0;
            if (state[i-(Gui.getDim()+1)] == 1) aliveNeighbours++;
            if (state[i-Gui.getDim()] == 1) aliveNeighbours++;
            if (state[i-(Gui.getDim()-1)] == 1) aliveNeighbours++;
            if (state[i-1] == 1) aliveNeighbours++;
            if (state[i+1] == 1) aliveNeighbours++;
            if (state[i+(Gui.getDim()-1)] == 1) aliveNeighbours++;
            if (state[i+Gui.getDim()] == 1) aliveNeighbours++;
            if (state[i+(Gui.getDim()+1)] == 1) aliveNeighbours++;

            if (aliveNeighbours == 3) {
                box[i].setBackground(BLACK);
                newstates[i] = 1;
            } else {
                box[i].setBackground(WHITE);
                newstates[i] = 0;
            }
        }
    }
    return newstates;
}
}

Answer 1

Yours is a classic case of a Swing threading issue, with here it being due to your having long-running code that also calls Thread.sleep(...) on the Swing event thread, which will put the entire GUI to sleep, certainly not your goal.

The solution is the same as any similar question (which you should have searched for and found before posting here): use a SwingWorker for background threading if you have long-running code, or a Swing Timer for calling code recurrently with delays.

Here which you use will depend on how slow Maths.render is. If this calculates very fast, then all you need is a Swing Timer to make this call intermittently and with delay. If this method takes a significant amount of time to perform, then you will need to go the SwingWorker route.

For example, timer code could look like:

private void gameLoop() {
  int timerDelay = 100;
  new Timer(timerDelay, new ActionListener() {
     private final int maxIndex = 20;
     private int index = 0;

     @Override
     public void actionPerformed(ActionEvent e) {
        if (index < maxIndex) {
           states = Maths.render(box, frame, states);
           frame.validate();
           frame.repaint();
      } else {
           ((Timer) e.getSource()).stop();
        }
        index++;
     }
  }).start();
}

Note that gameLoop should be a non-static instance method. I also did not allow parameter passage, but instead made these guys fields of the class:

private JPanel[] box;
private int[] states;

and made sure to set those fields:

public Gui(int[] states) {
  this.states = states;
  frame = new JFrame("Game of Life by Boris Verwoerd");

  baseFrame = new JPanel();
  baseFrame.setSize(500, 500);

  frame.add(baseFrame);

  base = new GridLayout(DIMENSION, DIMENSION);
  base.setHgap(-1);
  base.setVgap(-1);

  baseFrame.setLayout(base);

  box = new JPanel[DIMENSION * DIMENSION];

  for (int i = 0; i < (DIMENSION * DIMENSION); i++) {
     baseFrame.add(box[i] = new JPanel());
     box[i].setBorder(BorderFactory.createLineBorder(Color.black));
  }

  frame.setSize(500, 500);
  frame.setVisible(true);
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.setResizable(false);
  frame.validate();
  frame.repaint();

  gameLoop();
}