跳出循环，但需要保持运行？

Question

我已经绕了一个圈（在一个圆圈里），但现在我的应用程序不会继续执行其他任务，因为我陷入了一个循环。

如何摆脱这种情况，同时让我的圆圈在后台移动？

我知道这是因为我一直在调用方法 draw();，但是我应该如何保持绘制这个圆？

public class MyFrame extends JPanel {
        int xc = 150, yc = 150, r = 100, diam = 50;
        double inc = Math.PI/360, theta = 0;

        public void draw(Graphics g) {

                Timer timer = new Timer(0, new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent e) {
                                theta = theta+inc;
                                repaint();
                                System.out.println(theta);
                        }
                });
                timer.setDelay(20);
                timer.start();
        }
        @Override
        public void paint(Graphics g) {
                super.paintComponent(g);
                Graphics2D g2d = (Graphics2D) g;
                g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON ); //smooth the border around the circle
                g2d.rotate(theta, xc, yc);
                g2d.setColor(Color.blue);
                g2d.drawOval(xc + r - diam / 2, yc + r - diam / 2, diam, diam);
                draw(g);
        }
}

Answer 1

将循环、计时器与绘画分开。让定时器改变关键变量的状态，然后调用重绘。因此，您可以在绘画方法之外创建并启动 Timer ，例如在构造函数中，并让 paintComponent 专注于一件事和一件事，绘画，而不是改变状态:

public class MyPanel extends JPanel {
    int xc = 150, yc = 150, r = 100, diam = 50;
    double inc = Math.PI/360, theta = 0;
    
    public MyPanel () {
        Timer timer = new Timer(20, e -> {
            theta += inc;
            repaint();          
        });
        timer.start();
        
    }
    
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        
        Graphics2D g2d = (Graphics2D) g;
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON ); 
        g2d.rotate(theta, xc, yc);
        g2d.setColor(Color.blue);
        g2d.drawOval(xc + r - diam / 2, yc + r - diam / 2, diam, diam);
    }
}

跳出循环，但需要保持运行？

Getting out of a loop, but it needs to remain running?

java

animation

swing

move

jpanel