wrong output and exception problem

[oghenekaro EFEKODO]

need help in identifying what is wrong with my code especially the hypergeomeyric method which when ever i execute it,it display an understandable exception in command prompt.also the poisson method only display the correct result when r=0 but result when r=1 to n.thanks for ever listening hears.

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import java.awt.*;
import java.awt.event.*; 
import javax.swing.*; 
import javax.swing.JOptionPane;
import javax.swing.border.*;
public class CombGUI extends JPanel {
private JTextField outputField,binomialField,poissonField,
hypergeometricField,nF,pF,npoissonF,ppoissonF,
dField,nField,NField;
private JButton binomialbutton,poissonbutton,hypergeometricbutton;
private JPanel binomialpanel,poissonpanel,hypergeometricpanel,finalpanel;
public CombGUI(){
//setLayout(new FlowLayout(FlowLayout.CENTER)); 
JTabbedPane pane=new JTabbedPane();
pane.setPreferredSize(new Dimension(500,500));
//pane.addTab("Binomial Distribution",binomialpanel);
add(pane);

binomialpanel=new JPanel();
binomialpanel.setLayout(null);
binomialpanel.setBorder(new LineBorder(Color.red,10));
binomialpanel.setPreferredSize(new Dimension(250,250));


JLabel n=new JLabel("Enter sample value(n)");
n.setBounds(10,15,200,40);
binomialpanel.add(n);

nF=new JTextField(5);
nF.setBounds(180,15,40,40);
binomialpanel.add(nF);

JLabel p=new JLabel("Enter Prob. of Success(p)");
p.setBounds(10,60,250,40);
binomialpanel.add(p);

pF=new JTextField(5);
pF.setBounds(180,60,40,40);
binomialpanel.add(pF);

JLabel binomialLabel=new JLabel("Enter Recurance Value(r):");
binomialLabel.setBounds(10,100,250,40);
binomialpanel.add(binomialLabel);

binomialField=new JTextField(5);
binomialField.setBounds(180,100,40,40);

BiHandler b=new BiHandler();

binomialbutton=new JButton("Show Result");
binomialbutton.setBounds(40,200,140,40);
binomialbutton.addActionListener(b);

binomialpanel.add(binomialbutton);
binomialpanel.add(binomialField);

pane.addTab("Binomial Distribution",binomialpanel);
//pane.add(binomialpanel);


//begins poisson computation
poissonpanel=new JPanel();
poissonpanel.setLayout(null);
poissonpanel.setBorder(new LineBorder(Color.red,10));


JLabel npoisson=new JLabel("Enter Sample value(n)");
npoisson.setBounds(10,10,250,40);
poissonpanel.add(npoisson);

npoissonF=new JTextField(5);
npoissonF.setBounds(180,10,40,40);
poissonpanel.add(npoissonF);

JLabel ppoisson=new JLabel("Enter Prob. of success(p)");
ppoisson.setBounds(10,50,250,40);
poissonpanel.add(ppoisson);

ppoissonF=new JTextField(5);
ppoissonF.setBounds(180,50,40,40);
poissonpanel.add(ppoissonF);

JLabel poissonLabel=new JLabel("Enter Number of Ocurrance in Sample(r):");
poissonLabel.setBounds(10,90,250,40);
poissonpanel.add(poissonLabel);

poissonField=new JTextField(5);
poissonField.setBounds(260,90,40,40);
//poissonField.addActionListener(this);
poissonpanel.add(poissonField);

PoHandler po=new PoHandler();

poissonbutton=new JButton("Show Result");
poissonbutton.setBounds(40,200,140,40);
poissonbutton.addActionListener(po);

poissonpanel.add(poissonbutton);
pane.addTab("Poisson Distribution",poissonpanel);

//begins hypergeometric distribution
hypergeometricpanel=new JPanel();
hypergeometricpanel.setLayout(null);
hypergeometricpanel.setBorder(new LineBorder(Color.red,10));

JLabel NLabel=new JLabel("Enter Smaple Value(N):");
NLabel.setBounds(10,10,250,40);
hypergeometricpanel.add(NLabel);

JTextField NField=new JTextField(5);
NField.setBounds(180,10,40,40);
//NField.addActionListener(this);
hypergeometricpanel.add(NField);

JLabel nhLabel=new JLabel("Enter Distinctive Object(n):");
nhLabel.setBounds(10,50,250,40);
hypergeometricpanel.add(nhLabel);

JTextField nField=new JTextField(5);
nField.setBounds(180,50,40,40);
//nField.addActionListener(this);
hypergeometricpanel.add(nField);

JLabel dLabel=new JLabel("Enter Defective Ocurrance in Sample(d):");
dLabel.setBounds(10,90,250,40);
hypergeometricpanel.add(dLabel);

JTextField dField=new JTextField(5);
dField.setBounds(250,90,40,40);
//dField.addActionListener(this);
hypergeometricpanel.add(dField);

JLabel hypergeometricLabel=new JLabel("Enter Recurance Value(r):");
hypergeometricLabel.setBounds(10,130,250,40);
hypergeometricpanel.add(hypergeometricLabel);

JTextField hypergeometricField=new JTextField(5);
hypergeometricField.setBounds(180,130,40,40);
//hypergeometricField.addActionListener(this);
hypergeometricpanel.add(hypergeometricField);

HyHandler hy=new HyHandler();

hypergeometricbutton=new JButton("Show Result");
hypergeometricbutton.setBounds(40,200,140,40);
hypergeometricbutton.addActionListener(hy);

hypergeometricpanel.add(hypergeometricbutton);
pane.addTab("Hypergeometric Distribution",hypergeometricpanel);

}
public long factorial(int n){
long fact=1;
if(n==0)
return 1;
else
return n*factorial(n-1);
}
public long comb(int n,int r){
return factorial(n)/(factorial(r)*factorial(n-r));
}

//compute binomial distribution
public double binomial(int n,int r,double p){ 
//final int n=6;
//final double p=0.05;
 double q=(double)(1-p);
return (double)((long)comb(n,r)*(Math.pow((double)(p),r))*(Math.pow((q),(n-r))));
}

//compute poisson distribution
public double poisson(int n,int r,double p){
//final int n=40;
//final double p=0.02;
double y=(Math.pow((n*p),r)*Math.exp((-n*p)))/(long)factorial(r);
return y;
}

//compute hypergeometric distribution
public double hypergeometric(int N,int n,int d,int r){
//final int N=100;
//final int n=20;
//final int d=5;
return ((double)comb(d,r)*(double)comb((N-d),(n-r)))/(double)comb(N,n);
}

public static void main(String[] k){
CombGUI cm=new CombGUI(); 
JFrame f=new JFrame();
f.setSize(700,700);
f.setVisible(true);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container c=f.getContentPane();
c.add(cm);
} 
private class BiHandler implements ActionListener{
public void actionPerformed(ActionEvent e){
try{

int a1=Integer.parseInt(nF.getText());
int a3=Integer.parseInt(binomialField.getText());
double a2=Double.parseDouble(pF.getText());
if(e.getSource()==binomialbutton){
double  answer=(double)binomial(a1,a3,a2);
JOptionPane.showMessageDialog(CombGUI.this,Double.toString(answer),
"Binomial Distribution Result",JOptionPane.INFORMATION_MESSAGE);
}

}
catch(NumberFormatException exc){System.err.println(exc);}
}
}
private class PoHandler implements ActionListener{
public void actionPerformed(ActionEvent e){
try{
int bb1=Integer.parseInt(npoissonF.getText());
int bb3=Integer.parseInt(poissonField.getText());
double bb2=Double.parseDouble(ppoissonF.getText());
if(e.getSource()==poissonbutton){
double  poissonanswer=(double)poisson(bb1,bb3,bb2);
JOptionPane.showMessageDialog(CombGUI.this,Double.toString(poissonanswer),
"Poisson Distribution Result",JOptionPane.INFORMATION_MESSAGE);
}
}
catch(NumberFormatException ex){System.err.println(ex);}
}
}
private class HyHandler implements ActionListener{
public void actionPerformed(ActionEvent e){
try{
int c1=Integer.parseInt(NField.getText());
int c2=Integer.parseInt(nField.getText());
int c3=Integer.parseInt(dField.getText());
int c4=Integer.parseInt(hypergeometricField.getText());
if(e.getSource()==hypergeometricbutton){
double  answer2=(double)hypergeometric(c1,c2,c3,c4);
JOptionPane.showMessageDialog(CombGUI.this,Double.toString(answer2),
"Hypergeometric Distribution Result",JOptionPane.INFORMATION_MESSAGE);
}
}
catch(NumberFormatException ec){System.err.println(ec);}
}
}
}   
 

[David Nemeskey]

Hello,

please describe what exceptions you get with which parameters! It would be much easier to help like that.

Anyway, I have run your code, and I got the following exception when trying the Hypergeometric Distribution:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at JavaRanch.CombGUI$HyHandler.actionPerformed(CombGUI.java:240)

A short inspection told me that NField (and the others as well: nField, rField, etc) are null. Please have a look at the GUI building code. NField is declared as:

JTextField NField=new JTextField(5);
NField.setBounds(180,10,40,40);
//NField.addActionListener(this);
hypergeometricpanel.add(NField);

It is redefined locally, so no wonder that the NField member in the class is null. Compare this with the field initialization for the Poisson tab:

poissonField=new JTextField(5);
poissonField.setBounds(260,90,40,40);
//poissonField.addActionListener(this);
poissonpanel.add(poissonField);

These errors can be very annoying, but should not be hard to find. The exception above is very clear about what the problem is: a null reference in the actionPerformed method. So you should just find which reference is null. Using an IDE with a debugging option (nearly all of them) can help much, as it can show you which one is the culprit just by moving your mouse over them.
[ November 17, 2006: Message edited by: David Nemeskey ]

[David Nemeskey]

Also, one other suggestion:
in the main method, you should call f.setVisible() as the last instruction.

Why?

You may remember, that according to the Swing threading model, all modifications to an already visible GUI must be run in the event dispatch thread. This applies to your program from the moment you call f.setVisible(). When I first ran your program, it just displayed an empty frame, as the c.add(cm) "did not make it" to my screen.

Please have a look at the Swing tutorial at Sun.
[ November 17, 2006: Message edited by: David Nemeskey ]

[Craig Wood]

import java.awt.*;
import java.awt.event.*; 
import javax.swing.*; 
import javax.swing.border.*;
 
public class CombRx extends JPanel { 
    private JTextField outputField,binomialField,poissonField,
                       hypergeometricField,nF,pF,npoissonF,ppoissonF,
                       dField,nField,NField;
    private JButton binomialbutton,poissonbutton,hypergeometricbutton;
    private JPanel binomialpanel,poissonpanel,hypergeometricpanel,finalpanel; 
 
    public CombRx() { 
        JTabbedPane pane=new JTabbedPane();
        pane.setPreferredSize(new Dimension(500,500));
        add(pane);
 
        binomialpanel=new JPanel();
        binomialpanel.setLayout(null);
        binomialpanel.setBorder(new LineBorder(Color.red,10));
        binomialpanel.setPreferredSize(new Dimension(250,250));
 
        JLabel n=new JLabel("Enter sample value(n)");
        n.setBounds(10,15,200,40);
        binomialpanel.add(n);
 
        nF=new JTextField(5);
        nF.setBounds(180,15,40,40);
        binomialpanel.add(nF);
 
        JLabel p=new JLabel("Enter Prob. of Success(p)");
        p.setBounds(10,60,250,40);
        binomialpanel.add(p);
 
        pF=new JTextField(5);
        pF.setBounds(180,60,40,40);
        binomialpanel.add(pF);
 
        JLabel binomialLabel=new JLabel("Enter Recurance Value(r):");
        binomialLabel.setBounds(10,100,250,40);
        binomialpanel.add(binomialLabel);
 
        binomialField=new JTextField(5);
        binomialField.setBounds(180,100,40,40);
 
        BiHandler b=new BiHandler();
 
        binomialbutton=new JButton("Show Result");
        binomialbutton.setBounds(40,200,140,40);
        binomialbutton.addActionListener(b);
 
        binomialpanel.add(binomialbutton);
        binomialpanel.add(binomialField);
 
        pane.addTab("Binomial Distribution",binomialpanel);
 

        //begins poisson computation
        PoHandler po=new PoHandler();
        poissonpanel=new JPanel();
        poissonpanel.setLayout(null);
        poissonpanel.setBorder(new LineBorder(Color.red,10));
 
        JLabel npoisson=new JLabel("Enter Sample value(n)");
        npoisson.setBounds(10,10,250,40);
        poissonpanel.add(npoisson);
 
        npoissonF=new JTextField(5);
        npoissonF.setBounds(180,10,40,40);
        poissonpanel.add(npoissonF);
 
        JLabel ppoisson=new JLabel("Enter Prob. of success(p)");
        ppoisson.setBounds(10,50,250,40);
        poissonpanel.add(ppoisson);
 
        ppoissonF=new JTextField(5);
        ppoissonF.setBounds(180,50,40,40);
        poissonpanel.add(ppoissonF);
 
        JLabel poissonLabel=new JLabel("Enter Number of Ocurrance in Sample(r):");
        poissonLabel.setBounds(10,90,250,40);
        poissonpanel.add(poissonLabel);
 
        poissonField=new JTextField(5);
        poissonField.setBounds(260,90,40,40);
        poissonField.addActionListener(po);  // okay to do this
        poissonpanel.add(poissonField);
 

        poissonbutton=new JButton("Show Result");
        poissonbutton.setBounds(40,200,140,40);
        poissonbutton.addActionListener(po);
 
        poissonpanel.add(poissonbutton);
        pane.addTab("Poisson Distribution",poissonpanel);
 
        //begins hypergeometric distribution
        HyHandler hy=new HyHandler();
        hypergeometricpanel=new JPanel();
        hypergeometricpanel.setLayout(null);
        hypergeometricpanel.setBorder(new LineBorder(Color.red,10));
 
        JLabel NLabel=new JLabel("Enter Smaple Value(N):");
        NLabel.setBounds(10,10,250,40);
        hypergeometricpanel.add(NLabel);
 
        /*JTextField*/ NField=new JTextField(5);
        NField.setBounds(180,10,40,40);
        NField.addActionListener(hy);
        hypergeometricpanel.add(NField);
 
        JLabel nhLabel=new JLabel("Enter Distinctive Object(n):");
        nhLabel.setBounds(10,50,250,40);
        hypergeometricpanel.add(nhLabel);
 
        // These four local variable declarations were hiding
        // the member variables which remain null. These null
        // member variabes causing the NullPointerException in
        // actionPerformed. Removing the type allows the line
        // to instantiate the member variables.
        /*JTextField*/ nField=new JTextField(5);
        nField.setBounds(180,50,40,40);
        nField.addActionListener(hy);
        hypergeometricpanel.add(nField);
 
        JLabel dLabel=new JLabel("Enter Defective Ocurrance in Sample(d):");
        dLabel.setBounds(10,90,250,40);
        hypergeometricpanel.add(dLabel);
 
        /*JTextField*/ dField=new JTextField(5);
        dField.setBounds(250,90,40,40);
        dField.addActionListener(hy);
        hypergeometricpanel.add(dField);
 
        JLabel hypergeometricLabel=new JLabel("Enter Recurance Value(r):");
        hypergeometricLabel.setBounds(10,130,250,40);
        hypergeometricpanel.add(hypergeometricLabel);
 
        /*JTextField*/ hypergeometricField=new JTextField(5);
        hypergeometricField.setBounds(180,130,40,40);
        hypergeometricField.addActionListener(hy);
        hypergeometricpanel.add(hypergeometricField);
 

        hypergeometricbutton=new JButton("Show Result");
        hypergeometricbutton.setBounds(40,200,140,40);
        hypergeometricbutton.addActionListener(hy);
 
        hypergeometricpanel.add(hypergeometricbutton);
        pane.addTab("Hypergeometric Distribution",hypergeometricpanel);
    }
 
    public long factorial(int n) {
       return n == 0 ? 1 : n*factorial(n-1); 
    }
 
    public long comb(int n, int r) { 
        return factorial(n)/(factorial(r)*factorial(n-r)); 
    }
 
    /** compute binomial distribution
     * <a href="http://mathworld.wolfram.com/BinomialDistribution.html" target="_blank" rel="nofollow">http://mathworld.wolfram.com/BinomialDistribution.html</a>
     *               n!
     * P [r|n] = ---------- p^r (1 - p)^(n-r)
     *  p        r!(n - r)!
     */ 
    public double binomial(int n, int r, double p) { 
        //final int n=6;
        //final double p=0.05;
        double q = 1.0 - p; 
        return comb(n, r) * Math.pow(p, r) * Math.pow(q, n-r); 
    }
 
    /**
     * compute poisson distribution
     * <a href="http://mathworld.wolfram.com/PoissonDistribution.html" target="_blank" rel="nofollow">http://mathworld.wolfram.com/PoissonDistribution.html</a>
     * <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/math/poifcn.html" target="_blank" rel="nofollow">http://hyperphysics.phy-astr.gsu.edu/hbase/math/poifcn.html</a>
     * as n becomes large:
     * lambda = np
     *         lambda^r * e^-lambda
     * P (r) = --------------------
     *  p              r!
     */
    public double poisson(int n, int r, double p) {
        //final int n=40;
        //final double p=0.02;
        double lambda = n*p;
        return Math.pow(lambda, r) * Math.exp(-lambda) / factorial(r);
    }
 
    //compute hypergeometric distribution
    public double hypergeometric(int N, int n, int d, int r ){
        //final int N=100;
        //final int n=20;
        //final int d=5;
        return (comb(d, r) * comb(N-d, n-r))/comb(N, n);
    }
 
    public static void main(String[] k) { 
        CombRx cm=new CombRx(); 
        JFrame f=new JFrame(); 
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        Container c=f.getContentPane(); 
        c.add(cm); 
        f.pack();
        f.setLocation(200,100);
        f.setVisible(true);
    }
 
    private class BiHandler implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            try {
                int a1=Integer.parseInt(nF.getText());
                int a3=Integer.parseInt(binomialField.getText());
                double a2=Double.parseDouble(pF.getText());
                if(e.getSource()==binomialbutton) { 
                    // the binomial method returns a double
                    // so you don't need the cast
                    double answer=binomial(a1,a3,a2); 
                    JOptionPane.showMessageDialog(CombRx.this,Double.toString(answer),
                                                  "Binomial Distribution Result",
                                                  JOptionPane.INFORMATION_MESSAGE); 
                }
            } catch(NumberFormatException exc) {
                System.err.println(exc);
            }
        }
    }
 
    private class PoHandler implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            try {
                int bb1=Integer.parseInt(npoissonF.getText());
                int bb3=Integer.parseInt(poissonField.getText());
                double bb2=Double.parseDouble(ppoissonF.getText()); 
                if(e.getSource()==poissonbutton) { 
                    double poissonanswer=poisson(bb1,bb3,bb2); 
                    JOptionPane.showMessageDialog(CombRx.this,
                                                  Double.toString(poissonanswer),
                                                  "Poisson Distribution Result",
                                                  JOptionPane.INFORMATION_MESSAGE); 
                }
            } catch(NumberFormatException ex) {
                System.err.println(ex);
            }
        }
    }
 
    private class HyHandler implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            try {
                int c1=Integer.parseInt(NField.getText());
                int c2=Integer.parseInt(nField.getText());
                int c3=Integer.parseInt(dField.getText());
                int c4=Integer.parseInt(hypergeometricField.getText());
                if(e.getSource()==hypergeometricbutton) { 
                    double answer2=hypergeometric(c1,c2,c3,c4); 
                    JOptionPane.showMessageDialog(CombRx.this,Double.toString(answer2),
                                                  "Hypergeometric Distribution Result",
                                                  JOptionPane.INFORMATION_MESSAGE); 
                }
            } catch(NumberFormatException ec) {
                System.err.println(ec);
            }
        }
    }
}