Please help me to avoid this Exception.

Question

I have a JTextField which will accept only non-negative integer. To get the Document roll_doc for the constructor of JTextField
I have a class maxLengthText which will make sure that the JTextfield accepts only non-negative integer.
I have a problem while resetting the content of the JTextField. As I have made sure that only integers are allowed in my text field.
So while using setText(" "). The code executes the exception in my actionListener. I don't want this exceptuion to get executed when I reset the content of my JTextField using setText(String).
Please help. Suggest any workaround for this. Thanks in advance
The code is as follows:
package marksheet;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.BorderFactory;
import javax.swing.*;
import javax.swing.text.*;
public class SpringApplet1 extends JApplet implements ActionListener {
     JLabel l_instruction1;
     JLabel l_instruction2;
     JLabel l_instruction3;
     JLabel l_instruction4;
     JLabel l_instruction5;
     JLabel l_instruction6;
     JLabel l_instruction7;
     JLabel l_instruction8;
     JLabel l_space;
     JLabel label1;
     JLabel label2;
     JLabel label3;
     JLabel label4;
     JTextField text1;
     JTextField text2;
     JTextField text3;
     JTextField text4;
     JLabel l_name;
     JLabel l_fname;     
     JLabel l_course;
     JLabel l_specialization;
     JLabel l_batch;
     JLabel l_semester;
     JLabel l_rollno;
     JLabel l_enrolno;
     JTextField t_name;
     JTextField t_fname;
     JTextField t_rollno;
     JTextField t_enrollno;
     JComboBox cb_course;
     JComboBox cb_branch;
     JComboBox cb_batch;
     JComboBox cb_semester;
     JCheckBox c_parttime;
     JCheckBox c_fulltime;
     JButton Submit;
     JButton enterMarks;
     JButton reset;
     JTextField txtInt;
     JPanel p;
     JPanel p1;
     JPanel p2;
     JPanel p3;
     public void init () {
     l_space = new JLabel(" ");
     Document roll_doc = new maxLengthText(5); // set maximum length to 5
     Document enroll_doc = new maxLengthText(6); // set maximum length to 6
     t_rollno= new JTextField(roll_doc, "", 6);
     t_enrollno= new JTextField(enroll_doc, "", 7);
     Document name_doc = new maxLengthAlpha(15); // set maximum length to 15
     t_name = new JTextField(name_doc, "", 7);
     l_instruction1 = new JLabel("All names should be alphabets",JLabel.LEFT);
     l_instruction1.setForeground(Color.blue);
     l_instruction1.setVisible(false);
     l_instruction1.setVisible(true);
     l_instruction2 = new JLabel("Name can not be greater than 15 characters",JLabel.LEFT);
     l_instruction2.setForeground(Color.blue);
     l_instruction2.setVisible(false);
     l_instruction2.setVisible(true);
     l_instruction3 = new JLabel("Seperate firstname and last name with a 'space'",JLabel.LEFT);
     l_instruction3.setForeground(Color.blue);
     l_instruction3.setVisible(false);
     l_instruction3.setVisible(true);
     l_instruction4 = new JLabel("All marks are out of 100, Marks obtained are non-negative integers",JLabel.LEFT);
     l_instruction4.setForeground(Color.blue);
     l_instruction4.setVisible(false);
     l_instruction4.setVisible(true);
     l_instruction8 = new JLabel("Marks obtained can not be greater than 100 ",JLabel.LEFT);
     l_instruction8.setForeground(Color.blue);
     l_instruction8.setVisible(false);
     l_instruction8.setVisible(true);
     l_instruction5 = new JLabel("Roll number should be of length 5 and only numeric",JLabel.LEFT);
     l_instruction5.setForeground(Color.blue);
     l_instruction5.setVisible(false);
     l_instruction5.setVisible(true);
     l_instruction6 = new JLabel("Enrolment number should be of length 6 and only numeric",JLabel.LEFT);
     l_instruction6.setForeground(Color.blue);
     l_instruction6.setVisible(false);
     l_instruction6.setVisible(true);
     l_instruction7 = new JLabel("All fields are Mandatory",JLabel.LEFT);
     l_instruction7.setForeground(Color.blue);
     l_instruction7.setVisible(false);
     l_instruction7.setVisible(true);
     l_name = new JLabel("Name",JLabel.LEFT);
     l_name.setForeground(Color.blue);
     l_fname = new JLabel("Father's Name",JLabel.LEFT);
     l_fname.setForeground(Color.blue);
     l_course = new JLabel("Course",JLabel.LEFT);
     l_course.setForeground(Color.blue);
     l_specialization = new JLabel("Specialization",JLabel.LEFT);
     l_specialization.setForeground(Color.blue);
     l_batch = new JLabel("Batch",JLabel.LEFT);
     l_batch.setForeground(Color.blue);
     l_semester = new JLabel("Semester",JLabel.LEFT);
     l_semester.setForeground(Color.blue);
     l_rollno = new JLabel("Roll Number",JLabel.LEFT);
     l_rollno.setForeground(Color.blue);
     l_enrolno = new JLabel("Enrolment Number",JLabel.LEFT);
     l_enrolno.setForeground(Color.blue);
     //t_name = new JTextField(20);
     t_name.setEditable(true);
//     t_name.setBackground(Color.YELLOW);
     t_fname = new JTextField(20);
     t_fname.setEditable(true);
//     t_fname.setBackground(Color.YELLOW);
     //t_rollno = new JTextField(20);
     t_rollno.setEditable(true);
//     t_rollno.setBackground(Color.YELLOW);
     //t_enrollno = new JTextField(20);
     t_enrollno.setEditable(true);
//     t_enrollno.setBackground(Color.YELLOW);
     label1 = new JLabel("Data Structures",JLabel.LEFT);
     label1.setForeground(Color.blue);
     label1.setVisible(true);
     label2 = new JLabel("Compiler Design",JLabel.LEFT);
     label2.setForeground(Color.blue);
     label2.setVisible(true);
     label3 = new JLabel("Numerical Analysis",JLabel.LEFT);
     label3.setForeground(Color.blue);
     label3.setVisible(true);
     label4 = new JLabel("Discrete Matehmatics",JLabel.LEFT);
     label4.setForeground(Color.blue);
     label4.setVisible(true);
     text1 = new JTextField(20);
     text1.setEditable(false);
//     text1.setBackground(Color.green);
     text1.setVisible(true);
     text2 = new JTextField(20);
     text2.setEditable(false);
//     text2.setBackground(Color.green);
     text2.setVisible(true);
     text3 = new JTextField(20);
     text3.setEditable(false);
//     text3.setBackground(Color.green);
     text3.setVisible(true);
     text4 = new JTextField(20);
     text4.setEditable(false);
//     text4.setBackground(Color.green);
     text4.setVisible(true);
     String a_course[] =
          {" ","BE","MCA"};
     String a_branch[] =
          {" ","Computer Science","Electronics"};
     String a_batch[] =
          {" ","2000-2001","2001-2002","2002-2003","2003-2004","2004-2005"};
     String a_semester[] =
          {" ","I","II","III","IV","V","VI","VII","VIII"};
     cb_course = new JComboBox(a_course);
     cb_branch = new JComboBox(a_branch);
     cb_batch = new JComboBox(a_batch);
     cb_semester = new JComboBox(a_semester);
     c_parttime = new JCheckBox("Part Time");
     c_fulltime = new JCheckBox("Full Time");
     Submit = new JButton ("Generate Marksheet");
     Submit.setVisible(true);
//     Submit.addActionListener(this);
     enterMarks = new JButton ("Enter Marks");
     enterMarks.setVisible(true);
// enterMarks.addActionListener(this);
     reset= new JButton ("Reset");
     reset.setVisible(true);
//reset.addActionListener(this);
     p = new JPanel(new GridLayout(5,2,2,2));
p.setBorder(BorderFactory.createTitledBorder("Student Details"));
     p.add(l_name);
     p.add(t_name);
p.add(l_fname);
     p.add(t_fname);
p.add(l_rollno);
     p.add(t_rollno);
p.add(l_enrolno);
     p.add(t_enrollno);
     p.add(l_space);
     p.add(l_space);
     p1 = new JPanel(new GridLayout(0,2,2,2));
     p1.setBorder(BorderFactory.createTitledBorder("Course Details"));
     p1.add(l_course);
     p1.add(cb_course);
     p1.add(l_specialization);
     p1.add(cb_branch);
     p1.add(l_batch);
     p1.add(cb_batch);
     p1.add(l_semester);
     p1.add(cb_semester);
     p1.add(c_parttime);
     p1.add(c_fulltime);
     p1.add(reset);
     p1.add(enterMarks);
     p2 = new JPanel(new GridLayout(0,2,2,2));
     p2.setBorder(BorderFactory.createTitledBorder("Marks Details"));
     p2.add(label1);
     p2.add(text1);
     p2.add(label2);
     p2.add(text2);
     p2.add(label3);
     p2.add(text3);
     p2.add(label4);
     p2.add(text4);
     p2.add(Submit);
     p2.setVisible(true);
     p3 = new JPanel(new GridLayout(0,1,2,2));
     p3.setBorder(BorderFactory.createTitledBorder("Instructions"));
     p3.add(l_instruction1);
     p3.add(l_instruction2);
     p3.add(l_instruction3);
     p3.add(l_instruction4);
     p3.add(l_instruction8);
     p3.add(l_instruction5);
     p3.add(l_instruction6);
     p3.add(l_instruction7);
     JFrame f = new JFrame("Student Marksheet System");
f.getContentPane().setLayout(new GridLayout(2,2,3,3));
f.getContentPane().add(p3);
     f.getContentPane().add(p);
f.getContentPane().add(p1);
     f.getContentPane().add(p2);
     enterMarks.addActionListener(new ActionListener()
          public void actionPerformed(ActionEvent e)
               String message = "Are you sure all information is correct";
               String get_text1;
               String title = "Confirmation";
               int getcourseindex;
               int getbranchindex;
               int getsemesterindex;
               int getbatchindex;
               getcourseindex = cb_course.getSelectedIndex();
               getbranchindex = cb_branch.getSelectedIndex();
               getsemesterindex = cb_semester.getSelectedIndex();
               getbatchindex = cb_branch.getSelectedIndex();
               if (c_fulltime.isSelected() == false && c_parttime.isSelected() == false)
                    JOptionPane.showMessageDialog(null,"Atleast one mandatory field is missing","TextField",1);
                         return;
               if(getcourseindex == 0)
                         JOptionPane.showMessageDialog(null,"Atleast one mandatory field is missing","TextField",1);
                         return;
               if(getbranchindex == 0)
                         JOptionPane.showMessageDialog(null,"Atleast one mandatory field is missing","TextField",1);
                         return;
               if(getsemesterindex == 0)
                         JOptionPane.showMessageDialog(null,"Atleast one mandatory field is missing","TextField",1);
                         return;
               if(getbatchindex == 0)
                         JOptionPane.showMessageDialog(null,"Atleast one mandatory field is missing","TextField",1);
                         return;
               int n = JOptionPane.showConfirmDialog(null,message,title, JOptionPane.YES_NO_OPTION);
               if(n==0)
                    get_text1 = t_name.getText();
                    t_name.setEditable(false);
                    t_fname.setEditable(false);
                    t_rollno.setEditable(false);
                    t_enrollno.setEditable(false);     
                    cb_course.setEnabled(false);     
                    cb_branch.setEnabled(false);     
                    cb_batch.setEnabled(false);     
                    cb_semester.setEnabled(false);
                    reset.setEnabled(false);
     reset.addActionListener(new ActionListener()
          public void actionPerformed(ActionEvent e)
               String message = "Are you sure to reset the fields";
               String title = "Confirmation";
               int n = JOptionPane.showConfirmDialog(null,message,title, JOptionPane.YES_NO_OPTION);
               if(n==0)
                    Submit.setEnabled(true);
                    cb_course.setSelectedIndex(0);
                    cb_branch.setSelectedIndex(0);
                    cb_batch.setSelectedIndex(0);
                    cb_semester.setSelectedIndex(0);
                    t_rollno.setText("");
     Submit.addActionListener(new ActionListener()
          public void actionPerformed(ActionEvent e)
               String message = "Confirmation will generate the marksheet";
               String title = "Confirmation";
               int n = JOptionPane.showConfirmDialog(null,message,title, JOptionPane.YES_NO_OPTION);
               if(n==0)
                    Submit.setEnabled(true);
     c_parttime.addActionListener(new ActionListener()
          public void actionPerformed(ActionEvent e)
               if (c_fulltime.isSelected() == true)
                    c_fulltime.setSelected(false);
     c_fulltime.addActionListener(new ActionListener()
          public void actionPerformed(ActionEvent e)
               if (c_parttime.isSelected() == true)
                    c_parttime.setSelected(false);
f.pack();
f.setVisible(true);
     public void paint(Graphics g) {
     //Draw a Rectangle around the applet's display area.
g.drawRect(0, 0, size().width - 1, size().height - 1);
     public void actionPerformed(ActionEvent event){
     package marksheet;
     import javax.swing.*;
     import javax.swing.text.*;
     import java.awt.*;
     public class maxLengthText extends PlainDocument
          int maxVal=0;
          public maxLengthText(int maxLength)
               maxVal = maxLength;
          publ1ic void insertString(int offset, String str, AttributeSet a) throws BadLocationException
               if (getLength() + str.length() > maxVal)
                    return;
               else
                    try
                         if(!Double.isNaN(Double.parseDouble(str)))
                              super.insertString(offset, str, a);
                    catch(Exception e)
                         JOptionPane.showMessageDialog(null,"Numbers Only","TextField",1);
                         offset=0;
     }

Answer 1

When you post code, please use the [co[i]de][co[i]de] tags. There is a code button above the message textfield.