ask error load drawline

Question

I want to make program load line from database.I've been setting at database every coordinat using double .but im getting error when i try to load from database and want to drawline in jpanel it's didn't appear in my jpanel.how to fix it? this is my code.

    ArrayList<Shape> linesList = new ArrayList<Shape>();
    shape line = null;

    public void loadline(){
        while (rs.next()) {
            double x1 = rs.getDouble("coorX");     //getting coordinate
            double y1 = rs.getDouble("coorY");
            double x2 = rs.getDouble("coorX2");
            double y2 = rs.getDouble("coorY2");
           line =new Line2D.Double(x1,y1,x2,y2);
           linesList.add(line);
        repaint();
        revalidate();
        }
    }catch(Exception E){
JOptionPane.showMessageDialog(null, "error load data");
}
    }catch(Exception e){
        JOptionPane.showMessageDialog(null, "error sql");

    }}

and this is my paint component method

 protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g;
    g2d.setColor(birumuda);
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    for(Shape content : linesList){
        g2d.draw(content);
    }
}

you have to load value from JDBC to util.List, then to invoke paintComponent by JCOmponent.repaint, inside paintComponent to loop in vakues stored in util.List — mKorbel, Sep 18 '15 at 16:50
i got error in drawing line. @mKorbel how to invoke paint component by jcomponent repaint?can you give me example what should i do to fix it? — FRIDY, Sep 18 '15 at 17:00

score 3 · Accepted Answer · answered Sep 18 '15 at 16:50

3

This should throw a NullPointerException. Where do you initialize your g2d variable? Your graphics look to be done incorrectly. You should 1) read the data in within a background thread, and store it into a collection, probably an ArrayList. Once this is done, notify Swing on the event thread so that you can draw the data within a JPanel's paintComponent method. See the painting tutorial for more on Swing graphics.

answered Sep 18 '15 at 16:50

Hovercraft Full Of Eels

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can you give me example what should i do? – FRIDY Sep 18 '15 at 16:59
@FRIDY: something similar to my code in an answer to a similar question [here](http://stackoverflow.com/a/6105437/522444). – Hovercraft Full Of Eels Sep 18 '15 at 17:02
i've been edit my script now.like this.but why didn't appear now? – FRIDY Sep 18 '15 at 17:35
1

@FRIDY: hard to tell without runnable code. It could be that the linesList collection is empty when the component draws itself, it could be that the component is too small to show the lines. Your best bet at this time is to create and post a [mcve]. – Hovercraft Full Of Eels Sep 18 '15 at 21:24

ask error load drawline

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