Question

We override paint method like this

public void paint(Graphics g)
{
   g.drawString(msg,xpos,ypos);
}

If we have another method lets say a mousepressed event method

public void mousePressed(MouseEvent me)    
    {
        xpos=me.getX();  // msg, xpos and ypos are variables of class
        ypos= me.getY();
        msg="You pressed mouse";
        repaint();
    }

Why cant we call paint(Graphics g) rather than repaint() ?

Answer 1

You should probably try that. You will notice

1. You will have to get the Graphics object g somehow.
2. Calling paint in the body of an event handler is not a best practice because it causes the body of that method to execute on the GUI thread right away, so no more events can be processed until paint returns. OTOH, repaint schedules a paint event to occur at some convenient point in the future and does not make the GUI appear to hang. Granted, in your case, drawString isn’t terribly slow, but in general….

Here is the classic article on painting, from the Java people themselves.