I need Help with codes. It isn't working

Question

I had once writing a code for finding the factorial of a number in elementary programming with C. I tried to incorporate it into my work. However, it is not working.
Below are the major hitches:
1. I have a problem with entering two numbers by simply pressing the buttons. Once i try to input another number the second number displaces the first on the textfield. Which suffices to say that entering a two or three digit number via the buttons is not working.
2. What I intend to archieve is such once I have enter the numbers using the buttons i could get the factorial of whatever number i entered by simply pressing the n! button. Once i attempt pressing the n! button it displays error in the command prompt (a long list of error comments).
How should I Proceed.
Below is my full code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class PanFrame extends JFrame implements ActionListener
     JTextField jTfd =new JTextField(20);
     JButton jbtn7 = new JButton ("7");
     JButton jbtn8 = new JButton ("8");
     JButton jbtn9 = new JButton ("9");
     JButton jbtn4 = new JButton ("4");
     JButton jbtn5 = new JButton ("5");
     JButton jbtn6 = new JButton ("6");
     JButton jbtn1= new JButton ("1");
     JButton jbtn2 = new JButton ("2");
     JButton jbtn3 = new JButton ("3");
     JButton jbtn0 = new JButton ("0");
     JButton jbtnFT = new JButton ("n!");
     public PanFrame (String title)
               super (title);
               Panel pan1 = new Panel();
               getContentPane().setLayout(new FlowLayout ());
               pan1.add(jTfd);
               Panel pan2 = new Panel();
               getContentPane().setLayout (new GridLayout (4,5,2,2));
               pan2.add (jbtn7);
               pan2.add (jbtn8);
               pan2.add (jbtn9);
               pan2.add (jbtn4);
               pan2.add (jbtn5);
               pan2.add (jbtn6);
               pan2.add (jbtn1);
               pan2.add (jbtn2);
               pan2.add (jbtn3);
               pan2.add (jbtn0);
               pan2.add (jbtnFT);
               getContentPane().add(pan1);
               getContentPane().add(pan2);
               //adding the Listener     
               jTfd.addActionListener(this);
                       jbtn7.addActionListener(this);
               jbtn8.addActionListener(this);
               jbtn9.addActionListener(this);
               jbtn4.addActionListener(this);
               jbtn5.addActionListener(this);
               jbtn6.addActionListener(this);
               jbtn1.addActionListener(this);
               jbtn2.addActionListener(this);
               jbtn3.addActionListener(this);
               jbtn0.addActionListener(this);
               jbtnFT.addActionListener(this);
               validate();
               this.addWindowListener (new WindowAdapter()
                    public void windowClosing (WindowEvent we)
                              setVisible (false);
                              System.exit (0);
           public void actionPerformed(ActionEvent ae)
                    jTfd.setText(ae.getActionCommand());
               if(ae.getActionCommand()=="n!")
                              int num= Integer.parseInt(jTfd.getText());
                         int i;
                         long fact=1;
                         for(i=1; i<=num; i++)
                                   fact *=i;
                         jTfd.setText(String.valueOf(fact));
     public static void main (String arg [ ])
               PanFrame ObjFr = new PanFrame ("Two Panel in One Frame");
               ObjFr.setSize (400, 400);
               ObjFr.setVisible (true);
}bakes

Answer 1

Perhaps something like this?
private String tempText = "";
public void actionPerformed(ActionEvent ae) {
if (jTfd.replaceSelection( jbtn.getActionCommand()
) )=="n!") {
          tempText = "";
          long fact=1;
for(int i=1; i<=Integer.parseInt(jTfd.getText());
); i++)
               fact *=i;
          jTfd.setText(String.valueOf(fact));
     else {
tempText +=
+= ((JButton)ae.getSource()).getActionCommand();
          jTfd.replaceSelection(tempText);
           * // Alternately, you can try:
* jTfd.setText(jTfd.getText() +
) + ((JButton)ae.getSource()).getActionCommand());
     }}I tried out what you suggested above but it gave the following eror:
PanFrame.java103:cannot resolve symbol
symbol: variable jbtn
location: class PanFrame
if (jTfd.replaceSelection( jbtn.getActionCommand() )=="n!")
'void' type not allowed here
if (jTfd.replaceSelection( jbtn.getActionCommand() )=="n!")
I do not think "if(jTfd.replaceSelection(jbtn.getActionCommand())=="n!")"
is the correct way of expressing what i intend to archieve. When i first wrote it out it did not make sense to me but i could not find an alternative. so i said let me give it a triy.
i have also attempted to structure it this way
public void actionPerformed(ActionEvent ae)
               JButton jbtn = (JButton)ae.getSource();
               jTfd.replaceSelection( jbtn.getActionCommand() );
               if (ae.getSource()==jbtnFT)
                    int num= Integer.parseInt(jTfd.getText());
                         int i;
                         long fact=1;
                         for(i=1; i<=num; i++)
                                   fact *=i;
                         jTfd.setText(String.valueOf(fact));
          } the action i performed having structured it as stated above was: I pressed the button 5 and it displayed 5 in the textfield then i wanted to find the factorial of 5. so i pressed the (n!) button. instead of calculating the factorial of 5 and displaying the output in the textfield, the factorial symbol was displayed after the number 5 and error messages were displayed in the command prompt. i have tried to type out some of the messages below:
java.lang.NumberFormatException: For input string: "5n!" at java.lang.NumberFormat Exception.forInputString(NumberFormatException.java.48)
at java.lang.Integer.parseInt(Integer.java: 477)
at java.lang.Integer.parseInt(Integer.jaa:518)
at PanFrame.actionPerformed(Drum.java:107)
at javax.swing.AbstractButton.fireActionPerformed (AbstractButton.java:1786)
at javax.swing.AbstractButton$ForwardActionEvents.actionPerformed(AbstractButton.java:1839)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
Please could you do me favor i am posting the entire code below: copy it and run it then you can see the error messages in its entirety. It is quite lenghty was i tried to type out were jus the first few lines.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class PanFrame extends JFrame implements ActionListener
     JTextField jTfd =new JTextField(20);
     JButton jbtn7 = new JButton ("7");
     JButton jbtn8 = new JButton ("8");
     JButton jbtn9 = new JButton ("9");
     JButton jbtnFT = new JButton ("n!");
     JButton jbtn4 = new JButton ("4");
     JButton jbtn5 = new JButton ("5");
     JButton jbtn6 = new JButton ("6");
     JButton jbtn1= new JButton ("1");
     JButton jbtn2 = new JButton ("2");
     JButton jbtn3 = new JButton ("3");
     JButton jbtn0 = new JButton ("0");
     public PanFrame (String title)
               super (title);
               Panel pan1 = new Panel();
               getContentPane().setLayout(new FlowLayout ());
               pan1.add(jTfd);
               Panel pan2 = new Panel();
               getContentPane().setLayout (new GridLayout (4,5,2,2));
               pan2.add (jbtn7);
               pan2.add (jbtn8);
               pan2.add (jbtn9);
               pan2.add (jbtnFT);
               pan2.add (jbtn4);
               pan2.add (jbtn5);
               pan2.add (jbtn6);
               pan2.add (jbtn1);
               pan2.add (jbtn2);
               pan2.add (jbtn0);
               getContentPane().add(pan1);
               getContentPane().add(pan2);
               //adding the Listener     
               jTfd.addActionListener(this);
                       jbtn7.addActionListener(this);
               jbtn8.addActionListener(this);
               jbtn9.addActionListener(this);
               jbtnFT.addActionListener(this);
               jbtn4.addActionListener(this);
               jbtn5.addActionListener(this);
               jbtn6.addActionListener(this);
               jbtn1.addActionListener(this);
               jbtn2.addActionListener(this);
               jbtn3.addActionListener(this);
               jbtn0.addActionListener(this);
               validate();
public void actionPerformed(ActionEvent ae)
               JButton jbtn = (JButton)ae.getSource();
               jTfd.replaceSelection( jbtn.getActionCommand() );
               if (ae.getSource()==jbtnFT)
                    int num= Integer.parseInt(jTfd.getText());
                         int i;
                         long fact=1;
                         for(i=1; i<=num; i++)
                                   fact *=i;
                         jTfd.setText(String.valueOf(fact));
public static void main (String arg [ ])
               PanFrame ObjFr = new PanFrame ("Two Panel in One Frame");
               ObjFr.setDefaultCloseOperation(EXIT_ON_CLOSE);
               ObjFr.setSize (400, 400);
               ObjFr.setVisible (true);
}