Thread: How this GUI functions

Can anyone who is patient enough help me to understand this program much better.

/**
 * @(#)STIregformmodule.java
 *
 * STIregformmodule application
 *
 * @author 
 * @version 1.8 2012/10/6
 */
 
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
 
public class STIregformmodule extends JFrame {
   // Declare variables:
   // array lists
   String[] columnNames = {"GENDER", "NAME", "COURSE", "YEAR", "ID #"};
   Object[][] data = new Object[25][5];
 
   // table
   JTable table = new JTable(data, columnNames) {
      // sets the ability of the cells to be edited by the user
      public boolean isCellEditable(int row, int column) {
         return false; // returns false, cannot be edited
      }
   };
   // frames
   JFrame frame, frame1;
   // panels
   JPanel buttonPanel, buttonPanel2, tablePanel, addPanel, editPanel;
   // labels
   JLabel labelGender, labelName, labelCourse, labelYear, labelID;
   // text fields
   JTextField txtGender, txtName, txtCourse, txtYear, txtID;
   // buttons
   JButton btnAdd, btnEdit, btnDelete, btnAddInput, btnCancel;
   // additionals
   int keyCode, rowIndex, rowNumber, noOfStudents;
   // button handler
   ButtonHandler bh = new ButtonHandler();
 
   public STIregformmodule() {
      // setting/modifying table components
      table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
      table.getSelectionModel().addListSelectionListener(new RowListener());
      table.getColumnModel().getColumn(1).setPreferredWidth(200);
      table.getColumnModel().getColumn(3).setPreferredWidth(50);
      table.getTableHeader().setResizingAllowed(false);
      table.getTableHeader().setReorderingAllowed(false);
      JScrollPane scrollPane = new JScrollPane(table);
 
      // main buttons
      btnAdd = new JButton("ADD");
      btnAdd.addActionListener(bh);
      btnEdit = new JButton("EDIT");
      btnEdit.addActionListener(bh);
      btnEdit.setEnabled(false); // disables the component
      btnDelete = new JButton("DELETE");
      btnDelete.addActionListener(bh);
      btnDelete.setEnabled(false); // disables the component
 
      // with button Listeners
 
      // sub buttons
      btnAddInput = new JButton("Add");
      btnAddInput.addActionListener(bh);
      btnCancel = new JButton("Cancel");
      btnCancel.addActionListener(bh);
 
      // set label names
      labelGender = new JLabel(" Gender:");
      labelName = new JLabel("    Name:");
      labelCourse = new JLabel(" Course:");
      labelYear = new JLabel("      Year:");
      labelID = new JLabel("           ID:");
 
      // set text fields width
      txtGender = new JTextField(20);
      txtName = new JTextField(20);
      txtCourse = new JTextField(20);
      txtYear = new JTextField(20);
      txtYear.setDocument(new JTextFieldLimit(1)); // limits the length of
                                                   // input: max of 1
      txtYear.addKeyListener(keyListener); // accepts only numerals
      txtID = new JTextField(20);
      txtID.setDocument(new JTextFieldLimit(3)); // limits the length of input:
                                                 // max of 3
      txtID.addKeyListener(keyListener); // accepts only numerals
 
      // main frame
      // panel for the table
      tablePanel = new JPanel();
      tablePanel.setLayout(new BoxLayout(tablePanel, BoxLayout.PAGE_AXIS));
      tablePanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 0, 10));
      tablePanel.add(table.getTableHeader());
      tablePanel.add(table);
 
      // panel for the main buttons
      buttonPanel = new JPanel();
      buttonPanel.setLayout(new GridBagLayout());
      GridBagConstraints c = new GridBagConstraints();
 
      // positions the main buttons
      c.gridx = 0;
      c.gridy = 0;
      c.ipady = 20;
      c.insets = new Insets(10, 10, 10, 10);
      c.fill = GridBagConstraints.HORIZONTAL;
      buttonPanel.add(btnAdd, c);
      c.gridx = 0;
      c.gridy = 1;
      c.fill = GridBagConstraints.HORIZONTAL;
      c.ipady = 20;
      c.insets = new Insets(10, 10, 10, 10);
      buttonPanel.add(btnEdit, c);
      c.gridx = 0;
      c.gridy = 2;
      c.fill = GridBagConstraints.HORIZONTAL;
      c.ipady = 20;
      c.insets = new Insets(10, 10, 10, 10);
      buttonPanel.add(btnDelete, c);
      c.gridx = 0;
      c.gridy = 3;
      c.ipady = 20;
      c.insets = new Insets(10, 10, 10, 10);
      c.fill = GridBagConstraints.HORIZONTAL;
 
      frame = new JFrame("Student Database");
      frame.setVisible(true);
      frame.setResizable(false);
      frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
      frame.add(tablePanel, BorderLayout.CENTER);
      frame.add(buttonPanel, BorderLayout.EAST);
      frame.pack();
 
      // ADD frame
      // panel for adding
      addPanel = new JPanel();
      addPanel.setLayout(new GridBagLayout());
 
      // positions the components for adding
      // labels
      c.insets = new Insets(1, 0, 1, 1);
      c.gridx = 0;
      c.gridy = 0;
      addPanel.add(labelID, c);
      c.gridy = 1;
      addPanel.add(labelName, c);
      c.gridy = 2;
      addPanel.add(labelCourse, c);
      c.gridy = 3;
      addPanel.add(labelYear, c);
      c.gridy = 4;
      addPanel.add(labelGender, c);
      // text fields
      c.gridx = 1;
      c.gridy = 0;
      c.ipady = 1;
      addPanel.add(txtID, c);
      c.gridy = 1;
      c.ipady = 1;
      addPanel.add(txtName, c);
      c.gridy = 2;
      c.ipady = 1;
      addPanel.add(txtCourse, c);
      c.gridy = 3;
      c.ipady = 1;
      addPanel.add(txtYear, c);
      c.gridy = 4;
      c.ipady = 1;
      addPanel.add(txtGender, c);
 
      // panel for other necessary buttons
      buttonPanel2 = new JPanel();
      buttonPanel2.setLayout(new GridLayout(1, 1));
      buttonPanel2.add(btnAddInput);
      buttonPanel2.add(btnCancel);
 
      frame1 = new JFrame("Student Database");
      frame1.setVisible(false);
      frame1.setResizable(false);
      frame1.setDefaultCloseOperation(HIDE_ON_CLOSE);
      frame1.add(addPanel, BorderLayout.CENTER);
      frame1.add(buttonPanel2, BorderLayout.PAGE_END);
      frame1.pack();
   }// end
 
   KeyListener keyListener = new KeyListener() {
      public void keyTyped(KeyEvent e) {
      }
 
      public void keyPressed(KeyEvent e) {
         keyCode = e.getKeyCode();
 
         if (!(keyCode >= 48 && keyCode <= 57) && !(keyCode >= 96 && keyCode <= 105)
                  && !(keyCode >= 37 && keyCode <= 40) && !(keyCode == 127 || keyCode == 8)) {
            txtID.setEditable(false);
         }
      }
 
      public void keyReleased(KeyEvent e) {
         txtID.setEditable(true);
      }
   };
 
   class RowListener implements ListSelectionListener {
      public void valueChanged(ListSelectionEvent event) {
         if (event.getValueIsAdjusting()) {
            rowIndex = table.getSelectedRow();
            if (data[rowIndex][0] == null || data[rowIndex][0] == "") {
               btnEdit.setEnabled(false);
               btnDelete.setEnabled(false);
            } else {
               btnEdit.setEnabled(true);
               btnDelete.setEnabled(true);
            }
         }
      }
   }// end
 
   class ButtonHandler implements ActionListener {
      public void actionPerformed(ActionEvent e) {
         try {
            if (e.getActionCommand().equals("ADD")) {
               // text fields for Student input data
               txtGender.setText("");
               txtName.setText("");
               txtCourse.setText("");
               txtYear.setText("");
               txtID.setText("");
 
               frame1.setTitle("Add Student data"); // title bar name for add
               btnAddInput.setActionCommand("Add2");
               btnAddInput.setText("ADD");
 
               frame1.setVisible(true); // sets the visibility of frame1
            } else if (e.getActionCommand().equals("EDIT")) {
               txtID.setText(data[rowIndex][4] + ""); // will preview the ID
                                                      // input during Add
               txtName.setText(data[rowIndex][1] + ""); // will preview the Name
                                                        // input during Add
               txtCourse.setText(data[rowIndex][2] + ""); // will preview the
                                                          // Course input during
                                                          // Add
               txtYear.setText(data[rowIndex][3] + ""); // will preview the Year
                                                        // input during Add
               txtGender.setText(data[rowIndex][0] + ""); // will preview the
                                                          // Gender input during
                                                          // Add
 
               txtID.setEditable(false); // forbids the user to edit the entered
                                         // ID number
 
               frame1.setTitle("Edit Student data"); // title bar name for edit
               btnAddInput.setActionCommand("Edit2");
               btnAddInput.setText("ACCEPT");
 
               frame1.setVisible(true); // sets the visibility of frame1
            } else if (e.getActionCommand().equals("DELETE")) {
               int confirm = JOptionPane.showConfirmDialog(frame, "ARE YOU SURE?", "CONFIRM",
                        JOptionPane.YES_NO_OPTION);
 
               if (confirm == 0) {
                  rowIndex = table.getSelectedRow();
                  rowNumber = 0;
 
                  noOfStudents--;
                  for (int i = 0; i <= 10; i++) {
                     if (rowIndex != i && i <= noOfStudents) {
                        data[rowNumber][4] = data[i][4];
                        data[rowNumber][1] = data[i][1];
                        data[rowNumber][2] = data[i][2];
                        data[rowNumber][3] = data[i][3];
                        data[rowNumber][0] = data[i][0];
                        rowNumber++;
                     } else if (rowIndex != i && i > noOfStudents) {
                        data[rowNumber][4] = "";
                        data[rowNumber][1] = "";
                        data[rowNumber][2] = "";
                        data[rowNumber][3] = "";
                        data[rowNumber][0] = "";
                        rowNumber++;
                     }
                  }
                  if (noOfStudents == 50) // if the number of students id equal
                                          // to 50, can no longer add students
                     btnAdd.setEnabled(false);
                  else
                     btnAdd.setEnabled(true); // continues to add students if
                                              // not equal to 50
                  if (noOfStudents == 0) {
                     btnDelete.setEnabled(false);
                     btnEdit.setEnabled(false);
                  } else {
                     btnDelete.setEnabled(true);
                     btnEdit.setEnabled(true);
                  }
 
                  rowIndex = table.getSelectedRow();
                  if (data[rowIndex][0] == null || data[rowIndex][0] == "") {
                     btnEdit.setEnabled(false);
                     btnDelete.setEnabled(false);
                  } else {
                     btnEdit.setEnabled(true);
                     btnDelete.setEnabled(true);
                  }
 
                  table.updateUI();
 
               }
            } else if (e.getActionCommand().equals("Add2")) {
 
               if (txtID.getText().isEmpty() || txtName.getText().isEmpty()
                        || txtCourse.getText().isEmpty()// /
                        || txtYear.getText().isEmpty() || txtGender.getText().isEmpty()) {
                  JOptionPane.showMessageDialog(null, "PLEASE FILL IN THE BLANKS.", "ERROR!",
                           JOptionPane.ERROR_MESSAGE);
               } else {
                  int dup = 0;
                  for (int i = 0; i < 10; i++) {
                     if (txtID.getText().equals(data[i][0])) {
                        JOptionPane.showMessageDialog(null, "ID NUMBER ALREADY EXISTS.", "ERROR!",
                                 JOptionPane.ERROR_MESSAGE);
                        dup++;
                        break;
                     }
                  }
                  if (dup == 0) {
                     rowIndex = table.getSelectedRow();
                     data[noOfStudents][4] = txtID.getText();
                     data[noOfStudents][1] = txtName.getText();
                     data[noOfStudents][2] = txtCourse.getText();
                     data[noOfStudents][3] = txtYear.getText();
                     data[noOfStudents][0] = txtGender.getText();
 
                     table.updateUI();
                     frame1.dispose();
                     noOfStudents++;
                     if (noOfStudents == 50)
                        btnAdd.setEnabled(false);
                     else
                        btnAdd.setEnabled(true);
                     if (data[rowIndex][0] == null) {
                        btnEdit.setEnabled(false);
                        btnDelete.setEnabled(false);
                     } else {
                        btnEdit.setEnabled(true);
                        btnDelete.setEnabled(true);
                     }
                  }
               }
               table.updateUI();
            } else if (e.getActionCommand().equals("Edit2")) {
               if (txtID.getText().isEmpty() || txtName.getText().isEmpty()
                        || txtCourse.getText().isEmpty() || txtYear.getText().isEmpty()
                        || txtGender.getText().isEmpty()) {
                  JOptionPane.showMessageDialog(null, "INCOMPLETE INPUT.", "ERROR!",
                           JOptionPane.ERROR_MESSAGE);
               } else {
                  data[rowIndex][4] = txtGender.getText();
                  data[rowIndex][1] = txtName.getText();
                  data[rowIndex][2] = txtCourse.getText();
                  data[rowIndex][3] = txtYear.getText();
                  data[rowIndex][0] = txtID.getText();
                  frame1.dispose();
               }
 
               table.updateUI();
 
            } else if (e.getActionCommand().equals("Cancel")) {
               frame1.dispose();
            }
 
         } catch (Exception error) {
         }
 
      }
   }// end
 
   class JTextFieldLimit extends PlainDocument {
      private int limit;
 
      JTextFieldLimit(int limit) {
         super();
         this.limit = limit;
      }
 
      JTextFieldLimit(int limit, boolean upper) {
         super();
         this.limit = limit;
      }
 
      public void insertString(int offset, String str, AttributeSet attr)
               throws BadLocationException {
         if (str == null)
            return;
 
         if ((getLength() + str.length()) <= limit) {
            super.insertString(offset, str, attr);
         }
      }
   }// end
 
   public static void main(String[] args) {
      new STIregformmodule();
   }// end of main
 
}// end of class

Yeah I've read through it. Everything in it works fine. Basically the problem is I'm just a beginner I don't understand how the methods in it work . I'm trying to create a simpler GUI just like it. A simple add, edit and delete GUI that prints my saved data in an array.