Calling repaint from another class JFrame

Question

I'm trying to call repaint from another class. But it does not work. I have to draw on a frame.

public class Tester extends JFrame{

    public static dtest d ;
    public static void main(String[] args) {
        Tester t = new Tester();
        d = new dtest();
        test tnew = new test();
    }

    public static class dtest extends JFrame implements MouseMotionListener{
        public static int x,y;
        dtest()
        {
            super("title");
            setSize(500,500);
            setVisible(true);
            addMouseMotionListener(this);
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            x = e.getX();
            y = e.getY();
            repaint();
        }

        @Override
        public void mouseMoved(MouseEvent e) {
            // TODO Auto-generated method stub

        }

        public void paint(Graphics g)
        {
            System.out.println("I am called");
        }
    }

    public static class test {
        public test()
        {   
            for(int i = 0 ; i < 5 ; i++)
            {
                System.out.println("I am called from run");
                d.repaint();
            }
        }
    }

}

this prints

I am called from run

I am called from run

I am called from run

I am called from run

I am called from run

so it does not executing the paint() portion. d.repaint() is not working. why?

Answer 1

Take a look at this page and look at the first answer. It's a similar if not exact question to yours.

JFrame's paint() method has been deprecated. The compiler, or your IDE, should be complaining a bit, especially if you place the @Override tag directly above the method (use this to test if this method can be rewritten... aka what you're trying to do).

This means that its use has been discouraged and some functionality may have been removed. When using javax.swing, you'll want to learn the system completely about JPanels and JComponents. To paint something on a screen, you'll want to add a custom class that extends JPanel with the add(Component c) method. Then, override the paintComponent(Graphics g) method in that class. Make sure to have the first line in that method be super.paintComponent(g); so that the window can refresh itself.

For completeness:

public class MyWindow extends JFrame {

    MyPanel thePanel;

    public MyWindow(int x, int y) {
        setSize(x, y);
        thePanel = new MyPanel(x, y);
        this.add(thePanel);
    }

}

public class MyPanel extends JPanel {
    public MyPanel(int x, int y)
        setSize(x, y);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(ImageManager.getImage("Cute Puppy"), 40, 40, null); // Or whatever
    }
}

So, when the repaint() or revalidate() method is called on the MyWindow, the Panel will recieve a paintComponent call.

Please let me know in the comments if you need any additional help.

Edited:

Since you need to use MouseMotionListener, and I'm still not quite understanding the context and trouble of "I need to call repaint from another class"... I will try my best.

Firstly, check out this tutorial on the Oracle pages. Also, check out the others on GUI's. You'll learn a lot about organization and displaying that will make you realize how their system can work with yours.

Now, for your questions:

i have to use MouseMotionListener.

Not quite... it is a good way for set up but you can run a Thread (something that constantly runs methods over and over) to check the Mouse coordinates. You'll want to start doing this when you get into games and other miscellaneous applications.

new Thread() {
    public void run() {
        Point mouse;
        int mousex;
        int mousey;
        while (true) {
            mouse = MouseInfo.getPointerInfo().getLocation();
            mousex = mouse.x - theWindow.getLocationOnScreen().x - 3; // You'll need to get the 
                // x coordinate, subtract the window's x coordinate, and subtract 3 because of 
                // the blue border around a standard pc window.
            mousey = mouse.y - theWindow.getLocationOnScreen().y - 29; // 29 is top bar height
            SomeOtherClass.processMove(mousex, mousey);
        }
    }
}.start();

Next: I tried that with JPanel but i could not do that. If you read the tutorial at the top of my edit, you see they implement MouseMotionListener with ease.

Next: I prefer to do it with JFrame. If you wish to process the mouse in the JFrame, do the following: Have your JFrame the listener, but the JPanel be where the mouse data comes from. As follows:

public class MyWindow extends JFrame implements MouseMotionListener {
    public MyPanel thePanel;
    public int x;
    public int y;

    public MyWindow() {
        thePanel = new MyPanel();
        thePanel.addMouseMotionListener(this); 
            // Make this JFrame get called when the mouse                    
            // moves across the panel.
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        x = e.getX();
        y = e.getY();
        thePanel.repaint();
    }

    @Override
    public void mouseMoved(MouseEvent e) {
        // TODO Auto-generated method stub

    }
}

public class MyPanel extends JPanel {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Other painting stuff
    }
}

Next: Now i have to update the frame from another class. I could not find a way to update the GUI(the frame) from another class.

Simple. Since the JPanel is what needs to be updated, add the following method to the MyWindow class:

public void repaintWindow() {
    thePanel.repaint();
}

And add this to whenever you need to update it:

MyWindow theWindow = new MyWindow();
theWindow.repaintWindow();

Next: all the answers here extended JPanel. So i could not find my answer.

I apologize, but you NEED a panel. It is possible to do with JFrames, but if you want to start doing things raw and low-level, you need to learn how these things work by learning to read the oracle tutorials and the oracle documentation. For now, use JPanels in any ways I've shown you.

Next: from another class I have to draw something on JFrame.Is that possible?

Yes, indeed! Whenever you want to draw something:

MyWindow theWindow = new MyWindow();

Graphics g = theWindow.thePanel.getGraphics();
BufferedImage someRandomImage = SomeRandomClass.getRandomImage();
g.drawImage(someRandomImage, 200, 481, null);

theWindow.repaintWindow();

I really hope I've helped but to program in java you need to use the tools they give you, especially when it comes to high level things like Swing. There are tutorials everywhere for this stuff. Please read them before asking for specific help in the future.