Problem in reloading graphics object.

Hi,

I am very new to swing and java awt. I am trying an application where I have 2 panels in main container. First panel (p1)contains some data and a button , upon click of button, Second panel (p2) has to draw a graph based on the content of first panel.
To draw the graph I am creating another class called secondPanel and passing p2 in the constructor, to get the graphics object of p2 to draw the graph.
The problem I am getting is when I change the data and redo the graph it retains the old graph. As I understand it is because of the graphics object that I am getting from p2.
before passing object p2 to the constructor of SecondPanel, I am calling removeAll() and validate() on p2, however my graphics object is not recreated.
Really appreciate if someone can help me here. Here is the code snippet of SecondPanel.

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.font.FontRenderContext;
import java.awt.font.LineMetrics;
import java.awt.geom.AffineTransform;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.JPanel;

public class SecondPanel extends JPanel{

JPanel p ;
    public SecondPanel(JPanel panel){
        this.p = panel;
        p.removeAll();
        p.revalidate();
        paintComponent(p.getGraphics());
    }
   
    private Double[] years1;
    //private Double[] data1;
    
   /* public Double[] getData1() {
        return data1;
    }

public void setData1(Double[] data) {
        this.data1 = data;
    }*/

public Double[] getYears1() {
        return years1;
    }

public void setYears1(Double[] years) {
        this.years1 = years;
    }
    
    
    
   Double[] data2 =  new Double[5];//  { 230, 1340, 6500, 330 };
    int[] years = { 1995, 1996, 1997, 1998 };
     final int PAD  = 20;
    final int VPAD = 45;
    final int HPAD = 55;
    final int TICK  = 2;
    final int STICK = 3;
    
    //chnages by mamta
   Double[] data  =  GraphAppl2.dja.toArray(data2);
    int dataLength = GraphAppl2.dja.size();
      
    
protected void paintComponent(Graphics g) {
           Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        drawAxes(g2);
        // plot data
        Point2D.Double lastP = null;
        for(int j = 0; j < data.length; j++) {
            g2.setPaint(Color.red);
            
            Point2D.Double p = modelToView(j, data[j]);
            
            g2.fill(new Ellipse2D.Double(p.x-2, p.y-2, 4, 4));
            if(lastP != null) {
                g2.setPaint(Color.blue);
                g2.draw(new Line2D.Double(lastP, p));
            }
            lastP = p;
        }
    }
    
private void drawAxes(Graphics2D g2) {
        double w = p.getWidth();
        double h = p.getHeight();
        
       //  Double[] data2 = this.getData();
       
       System.out.println("data length is " + data.length); 
        
        double xInc = (w - HPAD-PAD)/(dataLength-1);
        
        
        int max = (int)Math.ceil(getMaxValue());
        
        
        double yInc = (h - PAD-VPAD)/max;
        // grid lines
        g2.setPaint(new Color(220,230,240));
        // vertical
        for(int j = 0; j <= data.length; j++) {
            double x = HPAD + j*xInc;
            g2.draw(new Line2D.Double(x, VPAD, x, h-VPAD));
        }
        // horizontal
        for(int j = 0; j <= max; j=j+max/data.length) {
            double y = PAD + j*yInc;
            g2.draw(new Line2D.Double(HPAD, y, w-HPAD, y));
        }
        // axes
        g2.setPaint(new Color(51,51,51));

// ordinate
        g2.draw(new Line2D.Double(HPAD, PAD, HPAD, h-VPAD));
        // tick marks
        for(int j = 0; j <= max; j=j+max/data.length) {
            double y = PAD + j*yInc;
            g2.draw(new Line2D.Double(HPAD, y, HPAD-TICK, y));
        }
        // labels
        Font font = g2.getFont().deriveFont(14f);
        g2.setFont(font);
        FontRenderContext frc = g2.getFontRenderContext();
        LineMetrics lm = font.getLineMetrics("0", frc);
     /*   for(int j = 0; j <= max; j=j+max/data.length) {
            String s = String.valueOf(max-j);
            float y = (float)(PAD + j*yInc + lm.getDescent());
            float width = (float)font.getStringBounds(s, frc).getWidth();
            float x = (float)(HPAD - TICK - STICK - width);
            g2.drawString(s, x, y);
        } */
        // title
        char[] chars = "big numbers".toCharArray();
        // May look better without the descent.
        float height = lm.getAscent() /*+ lm.getDescent()*/;
        float y0 = PAD + (float)((h - PAD-VPAD - height*chars.length)/2);
        float y = y0 + lm.getAscent();
        for(int j = 0; j < chars.length; j++) {
            g2.drawString(String.valueOf(chars[j]), STICK, y);
            y += /*lm.getDescent() +*/ lm.getAscent();
        }
        
        // abcissa
        g2.draw(new Line2D.Double(HPAD, h-VPAD, w-PAD, h-VPAD));
       
        // tick marks
        for(int j = 0; j <= data.length; j++) {
            double x = HPAD + j*xInc;
            g2.draw(new Line2D.Double(x, h-VPAD, x, h-VPAD+TICK));
        }
        // labels
      /*  for(int j = 0; j < data.length; j++) {
            String s = String.valueOf(years[j]);
            float width = (float)font.getStringBounds(s, frc).getWidth();
            float x = (float)(HPAD + j*xInc - width/2);
            y = (float)(h-VPAD + TICK + STICK + lm.getAscent());
            g2.drawString(s, x, y);
        }*/
        // title
        String s = "years";
        float width = (float)font.getStringBounds(s, frc).getWidth();
        float x = HPAD + (float)((w - HPAD-PAD - width)/2);
        y = (float)(h - STICK - lm.getDescent());
        g2.drawString(s, x, y);
    }

private double getMaxValue() {
        double max = -Double.MAX_VALUE;
        // Double[] data2 = this.getData();
       
        for(int j = 0; j < data.length; j++) {
            if(data[j] > max)
                max = data[j];
        }
        return max;
    }
    
    private Point2D.Double modelToView(double x, double y) {
        double w = p.getWidth();
        double h = p.getHeight();
        double tx = HPAD;
        double ty = h-VPAD;
        AffineTransform at = AffineTransform.getTranslateInstance(tx, ty);
        double xScale = (w - HPAD-PAD)/(data.length-1);
        int max = (int)Math.ceil(getMaxValue());
        double yScale = (h - PAD-VPAD)/max;
        at.scale(xScale, -yScale);
        Point2D.Double dst = new Point2D.Double();
        at.transform(new Point2D.Double(x, y), dst);
        return dst;
    }

}

In the main container here is my code of reloading p2
How can I reload the graphics. while using super.paintComponent(g), I am getting null pointer exception and I don't know whether graphics object obtained by super will fit my requirement.
Thanks in advance!!!.

Hi,

I'm not sure what are you trying to achive.
Let me summirize it:

SecondPanel extends JPanel

It's only member is JPanel

When SecondPanel is created, you add the ref from a foo JPanel

Afterwards you add the SecondPanel to foo

A bit complicated, don't you think? ;)
You should use a CardLayout (p1 vs. p2).

Anyhow ... usually an invalidate() and repaint() on the component should do the trick.

Regards,
Rok

Yeah it was a bit complicated . So I changed my approach instead of using another class, I am using an inner class that extends JPanel and it works. The code posted above was not working even with invalidate and repaint may be because I was not calling super.paintComponent(g); .I think this needs to be called for repainting graphics object.