使用重绘和计时器每秒旋转一行

Question

So I'm trying to rotate a line every second using a Timer and a paint method. However, I'm not quite sure whats going on. Here are some of the relevant methods:

public static ActionListener taskPerformer = new ActionListener() {

    public void actionPerformed(ActionEvent e) {
        Clock cl = new Clock();
        seconds++;
        cl.repaint();
    }
};


public void paint(Graphics g){
    super.paint(g);
    Graphics2D g2 = (Graphics2D) g;
    for(int c = 0; c<10; c++){
        g2.setPaint(Color.BLACK);
        g2.drawOval(90-c/2,90-c/2,500+c,500+c); //thick outlined circle
    }
    g2.setPaint(Color.WHITE);
    g2.fillOval(90,90,501,501);
    g2.setPaint(Color.BLACK);
    g2.rotate(Math.toRadians(seconds*6));
    g2.drawLine(340,340,340,90);    

}

The line remains stationary. However if I add

System.out.println("tick");

to my actionPerformed method, the command line spits out "tick" 3 times a second. Any ideas as to why these things are happening?

Some context:

public static int seconds = 0;
public static int minutes = 0;
public static int hours = 0;
public static Clock cl = new Clock();
private ActionListener taskPerformer = new ActionListener() {

    public void actionPerformed(ActionEvent e) {
        System.out.println("tick");
        seconds++;
        cl.repaint();
    }
};
public static Timer timer = new Timer(1000,taskPerformer);

public static void main(String[] args){
    Clock cl = new Clock();
    init();
    SwingUtilities.invokeLater(new Runnable(){
        public void run() {
            createAndShowGUI();
        }
    });
}
public static void init(){
    timer.start();
}
public Clock() {
    super("Clock");
    timer.addActionListener(taskPerformer);

}

Answer 1

You are creating a new clock at every tick:

public void actionPerformed(ActionEvent e) {
    Clock cl = new Clock();
    ...

Instead you should use an existing instance.

// A field in the class:
Clock cl = new Clock();
...

// removed static so that it can access cl
private ActionListener taskPerformer = new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        seconds++;
        cl.repaint();
    }
};

You could also make the clock a field in the action listener, if you do not need to access it elsewhere.

Also note that you generally should not be overriding paint() , but should override paintComponent() instead. More about custom painting in swing here.

Edit: Now that there's more code available, it's possible to say that if you make the clock and action listener static it should work. However , you need to start the timer after the relevant components are ready:

public static void main(String[] args){
    // Removed spurious clock here
    SwingUtilities.invokeLater(new Runnable(){
        public void run() {
            createAndShowGUI();
            // Start the timer once the components are ready
            init();
        }
    });
}

The above mentioned point about not creating a clock in the action listener still stands.