Help on java graph applet

[Ranie Riegram]

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
public class Marglida extends Applet implements ActionListener
{
TextField t1,t2, t3;
TextArea t4;
Label l1, l2, l3;
Button b1;
public void init()
{
t1 = new TextField(5);
t2 = new TextField(5);
t3 = new TextField(5);
t4 = new TextArea(5,25);
l1 = new Label ("A: ");
l2 = new Label ("B: ");
l3 = new Label ("C: ");
b1 = new Button ("Leysa j�fnuna!");
b1.addActionListener (this);
this.add (t1);
this.add (l1);
this.add (t2);
this.add (l2);
this.add (t3);
this.add (l3);
this.add (b1);
this.add (t4);

}
public void actionPerformed (ActionEvent e)
{
Double D1, D2, D3;
D1 = new Double( t1.getText() );
D2 = new Double( t2.getText() );
D3 = new Double( t3.getText() );
double d1, d2, d3;
d1 = D1.doubleValue();
d2 = D2.doubleValue();
d3 = D3.doubleValue();
double var1, var2, var3;
var1 = d1;
var2 = d2;
var3 = d3;
String gildi;
double x;
double svar, svar2;
x=Math.pow(d2,2) - 4*d1*d3;

if(x ==0){
svar = -d2/(2*d1);
gildi = "Ein lausn:" + svar;
}
else if ((Math.pow(d2,2) - 4*d1*d3) < 0) {
gildi = "Engin lausn";
}
else {
svar = (-d2+Math.sqrt(x))/(2*d1);
svar2 = (d2-Math.sqrt(x))/(2*d1);
gildi = "Tv�r lausnir: "+ svar + " og " + svar2;
}

t4.setText( gildi );
repaint();
}
public void paint( Graphics g ){
//hnitakerfi
//g.drawLine(x1,y1,x2,y2)
for( int i=-50; i<50; i+=1 ){
g.drawLine( 220+(i*10),220-((var1*(i*i)+(var2*i)+var3)*10),220+((i+1)*10),220-((var1*((i+1)*(i+1))+(var2*(i+1))+var3))*10);
g.drawLine(0,340,440,340); // x-�s
g.drawLine(220,140,220,580); // y-�s
// x-�s l�nur
g.drawLine(260,336,260,344);
g.drawLine(300,336,300,344);
g.drawLine(340,336,340,344);
g.drawLine(380,336,380,344);
g.drawLine(420,336,420,344);
g.drawLine(180,336,180,344);
g.drawLine(140,336,140,344);
g.drawLine(100,336,100,344);
g.drawLine(60,336,60,344);
g.drawLine(20,336,20,344);
// y-�s l�nur
g.drawLine(216,380,224,380);
g.drawLine(216,420,224,420);
g.drawLine(216,460,224,460);
g.drawLine(216,500,224,500);
g.drawLine(216,540,224,540);
g.drawLine(216,300,224,300);
g.drawLine(216,260,224,260);
g.drawLine(216,220,224,220);
g.drawLine(216,180,224,180);
g.drawLine(216,140,224,140);
//t�lur � hnitakerfi
// 1 til 5 � x-�s
g.drawString("5",417,355);
g.drawString("4",377,355);
g.drawString("3",337,355);
g.drawString("2",297,355);
g.drawString("1",257,355);
// -1 til -5 � x-�s
g.drawString("-1",176,355);
g.drawString("-2",136,355);
g.drawString("-3",96,355);
g.drawString("-4",56,355);
g.drawString("-5",16,355);
// 1 til 5 � y-�s
g.drawString("1",203,305);
g.drawString("2",203,265);
g.drawString("3",203,225);
g.drawString("4",203,185);
g.drawString("5",203,145);
// -1 til -5 � y-�s
g.drawString("-1",203,385);
g.drawString("-2",203,425);
g.drawString("-3",203,465);
g.drawString("-4",203,505);
g.drawString("-5",203,545);
// 000000000000000000000
g.drawString("0",222,352);

}
}
}

I can't get this thing to work, I need to make it able to paint a graph if you give the damm the thing there integers A,B,C as in Ax^2+Bx+C ... but as I've said, I can't get it to work.

[Craig Wood]

/*  <applet code="GraphingApplet" width="400" height="400"></applet>
 *  use: >appletviewer GraphingApplet.java
 */
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.text.NumberFormat;
 
public class GraphingApplet extends Applet
{
    public void init()
    {
        FunctionGraphingPanel panel = new FunctionGraphingPanel();
        GraphingControl control = new GraphingControl(panel);
        setLayout(new BorderLayout());
        add(control.getUIPanel(), "North");
        add(panel);
        add(control.getStatusPanel(), "South");
    }
 
    public static void main(String[] args)
    {
        Applet applet = new GraphingApplet();
        Frame f = new Frame();
        f.addWindowListener(new WindowAdapter()
        {
            public void windowClosing(WindowEvent e)
            {
                System.exit(0);
            }
        });
        f.add(applet);
        f.setSize(400,400);
        f.setLocation(590,325);
        applet.init();
        applet.start();
        f.setVisible(true);
    }
}
 
class FunctionGraphingPanel extends Panel
{
    double a, b, c;
    final int PAD;
    final int
        A = 0,
        B = 1,
        C = 2;
 
    public FunctionGraphingPanel()
    {
       a = 1;
       b = 1;
       c = 1;
       PAD = 20;
       setBackground(Color.black);
    }
 
    public void paint(Graphics g)
    {
        super.paint(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        int w = getWidth();
        int h = getHeight();
        g2.setPaint(Color.white);
        // ordinate
        g2.draw(new Line2D.Double(w/2, PAD, w/2, h - PAD));
        // ordinate tick marks
        double yInc = (h - 2*PAD)/50.0;
        double y = PAD;
        for(int i = 0; i <= 50; i++)
        {
            if(i % 5 == 0)
                g2.draw(new Line2D.Double(w/2-2, y, w/2+2, y));
            else
                g2.draw(new Line2D.Double(w/2-1, y, w/2+1, y));
            y += yInc;
        }
        // abcissa
        g2.draw(new Line2D.Double(PAD, h/2, w - PAD, h/2));
        // abcissa tick marks
        double xInc = (w - 2*PAD)/50.0;
        double x = PAD;
        for(int i = 0; i <= 50; i++)
        {
            if(i % 5 == 0)
                g2.draw(new Line2D.Double(x, h/2-2, x, h/2+2));
            else
                g2.draw(new Line2D.Double(x, h/2-1, x, h/2+1));
            x += xInc;
        }
        // labels
        xInc = (w - 2*PAD)/10f;
        yInc = (h - 2*PAD)/10f;
        float sx, sy;
        String s;
        for(int i = 0; i <= 10; i++)
        {
            sx = w/2 + 5;
            sy = (float)(PAD + i * yInc + 2);
            s = String.valueOf(5 - i);
            if(i != 5)
                g2.drawString(s, sx, sy);
            sx = (float)(PAD + i * xInc - 4);
            sy = h/2 + 12;
            s = String.valueOf(i - 5);
            if(i != 5)
                g2.drawString(s, sx, sy);
        }
        g2.setPaint(Color.red);
        // plot data
        xInc = (w - 2*PAD)/50.0;
        yInc = (h - 2*PAD)/50.0;
        double lastX = 0, lastY = 0;
        double square, linear, constant;
        for(int i = 0, j = -25; i <= 50; i++, j = i - 25)
        {
            x = PAD + i * xInc;
            square   = a * j * j * (h/2 - PAD)/(5*5*5);
            linear   = b * j * (h/2 - PAD)/25;
            constant = c * (h/2 - PAD)/5;
            y = h/2 - (square + linear + constant);
            if(i > 0)
                g2.draw(new Line2D.Double(lastX, lastY, x, y));
            lastX = x;
            lastY = y;
        }
    }
 
    public void modifyConstants(int id, double inc)
    {
        switch(id)
        {
            case A:
                a += inc;
                break;
            case B:
                b += inc;
                break;
            case C:
                c += inc;
        }
        repaint();
    }
 
    public double[] getConstantValues()
    {
        return new double[] { a, b, c };
    }
}
 
class GraphingControl
{
    FunctionGraphingPanel graphingPanel;
    Checkbox aCheck, bCheck, cCheck;
    Button plus, minus;
    Label aLabel, bLabel, cLabel;
    int checkFlag;
    NumberFormat nf;
 
    public GraphingControl(FunctionGraphingPanel fgp)
    {
        graphingPanel = fgp;
        checkFlag = 0;
        nf = NumberFormat.getNumberInstance();
        nf.setMaximumFractionDigits(2);
        CheckboxGroup group = new CheckboxGroup();
        aCheck = new Checkbox("a", true, group);
        bCheck = new Checkbox("b", false, group);
        cCheck = new Checkbox("c", false, group);
        ItemListener il = new ItemListener()
        {
            public void itemStateChanged(ItemEvent e)
            {
                if(aCheck.getState())
                    checkFlag = 0;
                if(bCheck.getState())
                    checkFlag = 1;
                if(cCheck.getState())
                    checkFlag = 2;
            }
        };
        aCheck.addItemListener(il);
        bCheck.addItemListener(il);
        cCheck.addItemListener(il);
        plus = new Button("plus");
        minus = new Button("minus");
        ActionListener al = new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                Button button = (Button)e.getSource();
                if(button == plus)
                    adjustConstants(0.1);
                if(button == minus)
                    adjustConstants(-0.1);
                updateLabels();
            }
        };
        plus.addActionListener(al);
        minus.addActionListener(al);
        aLabel = new Label("a = 1");
        aLabel.setAlignment(Label.CENTER);
        bLabel = new Label("b = 1");
        bLabel.setAlignment(Label.CENTER);
        cLabel = new Label("c = 1");
        cLabel.setAlignment(Label.CENTER);
    }
 
    private void adjustConstants(double inc)
    {
        graphingPanel.modifyConstants(checkFlag, inc);
    }
 
    private void updateLabels()
    {
        double[] values = graphingPanel.getConstantValues();
        switch(checkFlag)
        {
            case 0:
                aLabel.setText("a = " + nf.format(values[0]));
                break;
            case 1:
                bLabel.setText("b = " + nf.format(values[1]));
                break;
            case 2:
                cLabel.setText("c = " + nf.format(values[2]));
        }
        graphingPanel.repaint();
    }
 
    public Panel getUIPanel()
    {
        Panel panel = new Panel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(2,2,2,2);
        gbc.weightx = 1.0;
        panel.add(aCheck, gbc);
        panel.add(bCheck, gbc);
        panel.add(cCheck, gbc);
        panel.add(plus, gbc);
        panel.add(minus, gbc);
        return panel;
    }
 
    public Panel getStatusPanel()
    {
        Panel panel = new Panel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(2,2,2,2);
        gbc.weightx = 1.0;
        gbc.fill = gbc.HORIZONTAL;
        panel.add(aLabel, gbc);
        panel.add(bLabel, gbc);
        panel.add(cLabel, gbc);
        return panel;
    }
}

[Ranie Riegram]

It's veryvery nice... But the things is, I need to be able to choose (put in, that is the user) what A is, B is and C is as in Ax^2+Bx+C and also a textbox that tells you where the graph "cuts" the x-axis...
but once again... very very impressive

[Craig Wood]

What else can I do for you?

[Ranie Riegram]

really nothing, it�s amazing, I just realized how it worked... it still though nee do be able to make the thing figure out his Ax^2+Bx+C=0 find the possible sollutions