Question

Hi Experts: I have a class which extends JPanel now ShapePanel (Sp) this gets added to a normal JPanel (Container) which inturn gets Added To JFrame (Window). In the paintComponent method i draw a shape…. but the shape never persists after rendering. In the debugger i can see that it gets re-drawn every time i resize or something like that.

Now i overloaded the JPanel’s (Sp’s) paintComponent and added this

    super.paintComponent(g);        

    ShapeDrawerGui SdG = new ShapeDrawerGui((Graphics2D)this.getGraphics());
    //for(Shape s : ArrayOfShapes)
    {
        if(s instanceof Rectangle)
                SdG.Paint((Rectangle)s);
            else if(s instanceof Triangle)
                SdG.Paint((Triangle)s);
            else
                SdG.Paint((Circle)s);
    } //s is a custom-shape object

the graphics object comes from (obviously) the JPanel….

But the drawn image never stays on the panel – you see it for a split second and its gone…

I have done some searching but to no avail.

The actual Drawing

public ShapeDrawerGui(Graphics2D _g)
{
    g = _g;
    g.setColor(Color.Black);
}

@Override
public void Paint(Circle c) 
{
    g.drawArc(0, 0, 50, 50, 0, 360);
}

@Override
public void Paint(Triangle t) 
{        
    Polygon p = new Polygon();
    p.addPoint(0, 25);
    p.addPoint(0 , 50);
    p.addPoint(50, 50);       
    g.drawPolygon(p);
}

@Override
public void Paint(Rectangle r) 
{
    g.drawRect(0, 0, 50, 50);
}

Kind regards

Markus

Answer 1

..what is the difference between this.getGraphics and the g ..?

A GUI should repaint when it is told to do so, and use the Graphics object supplied to the paint(Graphics) or paintComponent(Graphics) method. That method could be called at any time by the GUI, to repaint after being behind another window, for example.

When you make a call to getGraphics() you are provided with a non-persistent graphics object that will disappear next paint.