如何减慢 java 中的程序执行速度？

Question

我创建了一个 JavaFX 程序来递归地绘制 Sierpinski 地毯，但我想查看递归函数的运行情况，即减慢程序的速度以实时查看它的绘制。为此，我尝试了这样的事情：

public void pause(int sleepTime)
{
    try
    {
        Thread.sleep(sleepTime);
    }
    catch(InterruptedException e)
    {
        System.err.println("Error in running rotation animation!");
        System.exit(-1);
    }
}

然后我在我的 drawSierpinskiCarpet 函数中调用了这个函数，如下所示：

public void drawSeripinskiCarpet(GraphicsContext gc, int x, int y, int width, int height)
{
    if(width != height || width < 3)
        return;

    int size = width /= 3;
    gc.setFill(colors[index]);
    gc.fillRect(x + size, y + size, size, size);

    index++;

    if(index == colors.length)
    {
        index = 0;
    }

    pause(1);


    for(int i = 0 ; i < 3 ; i++)
    {
        for(int j = 0 ; j < 3 ; j++)
        {
            if(i == 1 && j == 1)
            {
                continue;
            }

            drawSeripinskiCarpet(gc, x + j * size, y + i * size, size, size);
        }
    }
}

但是程序挂了几秒钟，然后直接出现了地毯。我看不到正在执行的程序。

Answer 1

对 GUI 的任何修改只会在修改后产生视觉结果 returns。同时，JavaFX 无法处理任何事件并冻结，直到您的操作完成。

您可以使用 Timeline 一次执行一个操作：使用堆栈数据执行一次绘图；这允许您一次执行一个绘图操作，此外还可以为 Timeline.

的每一帧修改堆栈

@Override
public void start(Stage primaryStage) throws IOException {
    Canvas canvas = new Canvas(729, 729);
    final GraphicsContext gc = canvas.getGraphicsContext2D();

    Scene the_scene = new Scene(new StackPane(canvas));

    primaryStage.setScene(the_scene);
    primaryStage.show();

    final Color[] colors = new Color[] { Color.BLUE, Color.ORANGE, Color.GREEN, Color.RED, Color.BROWN,
            Color.MAGENTA, Color.YELLOW, Color.CYAN, Color.BLACK };
    class IndexHolder {
        int index = 0;

        Color getNextFill() {
            Color fill = colors[index];
            ++index;
            if (index >= colors.length) {
                index = 0;
            }
            return fill;
        }
    }
    final IndexHolder indexHolder = new IndexHolder();

    class StackEntry {
        int x;
        int y;
        int size;

        public StackEntry(int x, int y, int size) {
            this.x = x;
            this.y = y;
            this.size = size;
        }

        void executeStep(List<StackEntry> stack, IndexHolder indexHolder, GraphicsContext gc) {
            int size = this.size /= 3;
            gc.setFill(indexHolder.getNextFill());
            gc.fillRect(x + size, y + size, size, size);

            if (size >= 3) {
                // add new "calls" in reverse order here
                // (first call in original needs to be popped from the stack first)
                for (int i = 2; i >= 0; --i) {
                    for (int j = 2; j >= 0; --j) {
                        if (i == 1 && j == 1) {
                            continue;
                        }

                        stack.add(new StackEntry(x + j * size, y + i * size, size));
                    }
                }
            }
        }
    }

    // finally create the animation
    final List<StackEntry> stack = new ArrayList<>();
    stack.add(new StackEntry(0, 0, (int) canvas.getHeight()));

    final Timeline timeline = new Timeline();
    timeline.setCycleCount(Animation.INDEFINITE);
    timeline.getKeyFrames().add(new KeyFrame(Duration.millis(1),
            evt -> {
                // pop
                StackEntry entry = stack.remove(stack.size() - 1);

                entry.executeStep(stack, indexHolder, gc);
                if (stack.isEmpty()) {
                    timeline.stop();
                }
            }));

    timeline.play();

}

如何减慢 java 中的程序执行速度？

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