Knute Snortum

Thanks, that did it!

Hello all,

I am writing a proof-of-concept class to determine how to pause and resume a thread doing a cyclical process in Swing. The idea is to have an instance field called paused that the thread polls.  When the field is true, thread process will call Object.wait() to pause.  Then when the main proccess wants to resume, the paused field is set to false and an Object.notify() is called.

The thread process pauses just fine but when it comes to resuming, it never sees the notify() from the main process. Any help would be welcome.  Below is my code.
package swing; import java.awt.BorderLayout; import java.awt.event.ItemEvent; import java.awt.event.ItemListener; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JToggleButton; import javax.swing.SwingUtilities; public class ThreadCommunication extends JFrame { private static final long serialVersionUID = -3326890771329640907L; private int counter = 0; private boolean paused = false; private volatile Thread counterThread; public ThreadCommunication() { setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setSize(100, 100); setLocationRelativeTo(null); setLayout(new BorderLayout()); JLabel counterLabel = new JLabel("0", JLabel.CENTER); add(counterLabel, BorderLayout.CENTER); JToggleButton pauseButton = new JToggleButton("Pause"); add(pauseButton, BorderLayout.SOUTH); setVisible(true); counterThread = new Thread(() -> { while (true) { counterLabel.setText(String.valueOf(counter)); counter++; try { Thread.sleep(300); if (paused) { System.out.println("In counterThread, waiting"); // debug synchronized(this) {                    while (paused) {                        wait();                        System.out.println("  not waiting"); // debug                    }                } } } catch (InterruptedException e) { } } }); counterThread.setDaemon(true); counterThread.start(); pauseButton.addItemListener(new ItemListener() { @Override public synchronized void itemStateChanged(ItemEvent event) { System.out.println("In itemStateChange..."); // debug if (event.getStateChange() == ItemEvent.SELECTED) { // communicate pause to thread System.out.println("  paused"); // debug paused = true; } else { // communicate resume to thread System.out.println("  resume"); // debug paused = false; notify(); } } }); } public static void main(String[] args) { SwingUtilities.invokeLater(() -> { new ThreadCommunication(); }); } }

I wrote:I now have instructions to be able to pause the generation display, unpause, and restart, meaning to wipe the "universe" clean and start with a new random universe.

From my research it looks like I will have to run the evolve code in a Thread and communicate to that thread from the EDT.  I'm not good at Threads.  Maybe I should start a new topic since we're talking about something different than the subject of this topic?

Rob Camick wrote:Also in your painting code I question if you need:

               } else {                    g.drawRect(column * pixelsPerSide, row * pixelsPerSide, pixelsPerSide, pixelsPerSide);                }
since the drawing of the gridlines should paint the outline of each cell.

At least the painting looks the same to me when I remove the code.

That's weird, because when I remove that line, almost all the grid line disappear.  I am on Linux Ubuntu, if that makes a difference.

Rob Camick wrote:Even though you stop updating the panel after a fixed number of generations the Timer still fires events.

You can stop the Timer with code like:

       timer = new Timer(GlobalData.TIME_BETWEEN_GENERATIONS, event ->{            evolveOneGeneration(universe);            universe.setGenerationNumber(generation);            universeView.print(universe);            generation++;            if (generation > GlobalData.NUMBER_OF_GENERATIONS) {                Timer timer = (Timer)event.getSource();                timer.stop();            }        });

Thank you, this works.  However, I now have instructions to be able to pause the generation display, unpause, and restart, meaning to wipe the "universe" clean and start with a new random universe.  Timer has a restart, but this is different than what I need.  There doesn't seem to be pause and unpause methods.  Is there an idiom in Swing for pausing the event loop?  Someone here said Thread.sleep() and Swing don't play well together, and that seems to be the case, as this code just freezes the UI:
               while (data.getState() == GameOfLifeState.PAUSED) {                    try {                        Thread.sleep(10);                    } catch (InterruptedException e) {                        break;                    }                }

Rob Camick wrote:

there are noticeable pauses between each time the screen repaints)

That is because you have the "time to generations" set to 300. Try something like 15 to increase the animation.

Decreasing the time between generations doesn't change the effect.  Say we're at 300 ms.  I will see two or three generations go by with 300 ms between them.  Then I will see a generation that takes 500 ms or so, then two or three at 50 ms and so on.  This effect seems to go away after about 100 generations, so it may have to do with caching.

Updated my code so that it both starts by the SwingUtilities.invokeLater() and uses the Swing Timer.  The display is "correct" (no distortion of the graphics) but still jerky (there are noticeable pauses between each time the screen repaints).  I have updated GitHub.

Okay, I just tried this:
public class Main {    public static void main(String[] args) {        UIManager.put("swing.boldMetal", Boolean.FALSE);        SwingUtilities.invokeLater(() -> {            new GameOfLife();        });    } } ... and the display was messed up.  The text part (JLabels) didn't display until the last generation was done, and the graphical part was shifted a few pixels ro the right.  I have no idea why this would be so.

I saw that bit of code on some examples and not on others so I "tried" it and it "didn't work."  I know that's vague but it was many iterations ago in the version of my code.  I'll try launching with the invokeLater()  now in conjunction with  timer code and see how that works.

Campbell: just saw you post.  My understanding is that double-buffering is enabled by default.  Is that correct?

Yes, that did it!  Thanks!

I still have the problem of the screen updating in a "jerky" manner.  Instead of using gameOfLifePanel.repaint() I used gameOfLifePanel.paintImmediately(0, 0, length, length).  This improved things, but not entirely.  

I was thinking of painting everything all over again for each generation, but would this cause a flicker?  I'll give it a try.

Hi all,

I am trying to create a Swing GUI for the Game of Life implementation I wrote.  This is a challenge from https://hyperskill.org, so it comes with some restrictions, such as I have to have a class called "GameOfLife" that extends JFrame.  I hear that's not the best way to do things, but oh well.

So the problem.  In the Game of Life, you have an n x n grid with cells that die or come to life based on some simple rules.  My problem is how to display this correctly. I currently have a GameOfLifeGrid class that extends JPanel that prints lines in a nice grid.  Then I have another class, GameOfLifeCell, that extends JPanel and draws a filled square when the cell is "alive" and clears when it's dead. I have an array of arrays of GameOfLifeCells that correspond to a similar structure of booleans that inform me whether to make the filled square visible or not.

Problem is, it doesn't work.  First, the cells don't line up with the grid.  Second, I can only get one cell to become visible.  It's not always the same cell, though.  I have the whole application at https://github.com/ksnortum/game-of-life, but here are some snippets:

[Edit: the above URL now points to the latest version.  To see the version at the point in time this post was written, see https://github.com/ksnortum/game-of-life/tree/8dd7e1015bc884a332d50c43630566d9747fb4f6 ]

public class GameOfLife extends JFrame { // ...    private Data buildGui() {        // ...            JPanel graphicDisplay = new JPanel(new FlowLayout(FlowLayout.LEFT));        GameOfLifeGrid gridPanel = new GameOfLifeGrid();        int side = GlobalData.SIDE;        GameOfLifeCell[][] cells = new GameOfLifeCell[side][side];        for (int row = 0; row < side; row++) {            for (int column = 0; column < side; column++) {                GameOfLifeCell cell = new GameOfLifeCell(column * side, row * side, CellStatus.FILL);                cell.setVisible(false);                gridPanel.add(cell);                cells[row][column] = cell;            }        }        data.setCells(cells);        graphicDisplay.add(gridPanel);        add(graphicDisplay);                return data;    } }
public class GameOfLifeCell extends JPanel {    private final int side = GlobalData.SIDE;    private final int x;    private final int y;    private final CellStatus status;    public GameOfLifeCell(int x, int y, CellStatus status) {        this.x = x;        this.y = y;        this.status = status;        setOpaque(false);        int length = side * GlobalData.PIXELS_PER_SIDE;        setPreferredSize(new Dimension(length + 2, length + 2));    }    @Override    protected void paintComponent(Graphics g) {        super.paintComponent(g);        g.setColor(Color.BLACK);        if (status == CellStatus.DRAW) {            // This is not used.  I use setVisible() instead            g.drawRect(x, y, side, side);        } else if (status == CellStatus.FILL) {            g.fillRect(x, y, side, side);        }    } }
public class Universe {    private final int side = GlobalData.SIDE;    private boolean[][] universeMatrix;    private int generationNumber;    public void createUniverse() {        universeMatrix = new boolean[side][side];        generationNumber = 1;        Random random = new Random();        for (int row = 0; row < side; row++) {            for (int column = 0; column < side; column++) {                universeMatrix[row][column] = random.nextBoolean();            }        }    }        // ... }
public class UniverseView {    // ...    public void print(Universe universe) {            // ...                int side = GlobalData.SIDE;        GameOfLifeCell[][] cells = data.getCells();        boolean[][] matrix = universe.getUniverseMatrix();        for (int row = 0; row < side; row++) {            for (int column = 0; column < side; column++) {                cells[row][column].setVisible(matrix[row][column]);            }        }        try {            Thread.sleep(GlobalData.TIME_BETWEEN_GENERATIONS);        } catch (InterruptedException ignored) {        }    } }

You're right.  Sorry.

Could be, but it's a long shot.  I have a very basic built-in video card on the Linux box I tested the code on.