اريدشرح لهذا السورس

package stock;
import java.sql.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Framereport extends JFrame {
  Connection con;
    ResultSet rset,rset1;
    Statement stat,stat1;
    String url="jdbc:odbc:stock";
    String query;
     public int maingroupcode,subgroupcode,itemcode;

   public boolean newGroup=false;
  JTextField jTItemBlanace = new JTextField();
  JLabel jLabel3 = new JLabel();
  JLabel jLabel4 = new JLabel();
  JLabel jLabel5 = new JLabel();
  JComboBox jComboMainGroups = new JComboBox();
  JComboBox jComboSubGroups = new JComboBox();
  JComboBox jComboItems = new JComboBox();
  JLabel jLabel6 = new JLabel();
  JLabel jLabel7 = new JLabel();
  JTextField jt10 = new JTextField();
  JTextField jt9 = new JTextField();
  JTextField jt6 = new JTextField();
  JLabel jLabel9 = new JLabel();
  JLabel jLabel11 = new JLabel();
  JLabel jLabel8 = new JLabel();
  JTextField jTItemBlanace1 = new JTextField();

  public Framereport() {
    try {
      jbInit();
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }
  public static void main(String[] args) {
    Framereport framereport = new Framereport();
  }
  private void jbInit() throws Exception {
    this.getContentPane().setLayout(null);
    jTItemBlanace.setText("");
    jTItemBlanace.setBounds(new Rectangle(349, 98, 95, 21));
    jLabel3.setFont(new java.awt.Font("Dialog", 1, 13));
    jLabel3.setText("الفئه الرئسيه");
    jLabel3.setBounds(new Rectangle(465, 21, 77, 29));
    jLabel4.setBounds(new Rectangle(465, 48, 79, 29));
    jLabel4.setFont(new java.awt.Font("Dialog", 1, 13));
    jLabel4.setText("الفئه الفرعيه");
    jLabel5.setBounds(new Rectangle(467, 73, 73, 29));
    jLabel5.setFont(new java.awt.Font("Dialog", 1, 13));
    jLabel5.setText("الصنف");
    jComboMainGroups.setBounds(new Rectangle(330, 30, 116, 21));
    jComboMainGroups.addItemListener(new Framereport_jComboMainGroups_itemAdapter(this));

    jComboSubGroups.setBounds(new Rectangle(329, 52, 116, 21));
    jComboSubGroups.addItemListener(new Framereport_jComboSubGroups_itemAdapter(this));

    jComboItems.setBounds(new Rectangle(290, 75, 154, 21));
    jComboItems.addItemListener(new Framereport_jComboItems_itemAdapter(this));
    jComboItems.addItemListener(new Framereport_jComboItems_itemAdapter(this));

    jLabel6.setText("سعر الوحدة");
    jLabel6.setFont(new java.awt.Font("Dialog", 1, 13));
    jLabel6.setBounds(new Rectangle(462, 94, 73, 24));
    jLabel7.setText("نوع العهده");
    jLabel7.setHorizontalAlignment(SwingConstants.CENTER);
    jLabel7.setBorder(null);
    jLabel7.setForeground(Color.black);
    jLabel7.setFont(new java.awt.Font("Dialog", 1, 14));
    jLabel7.setBounds(new Rectangle(473, 225, 55, 22));
    jt10.setHorizontalAlignment(SwingConstants.RIGHT);
    jt10.setText("");
    jt10.setBorder(null);
    jt10.setFont(new java.awt.Font("Dialog", 1, 14));
    jt10.setBounds(new Rectangle(320, 185, 131, 24));
    jt9.setHorizontalAlignment(SwingConstants.RIGHT);
    jt9.setText("");
    jt9.setBorder(null);
    jt9.setFont(new java.awt.Font("Dialog", 1, 14));
    jt9.setBounds(new Rectangle(83, 154, 367, 23));
    jt6.setHorizontalAlignment(SwingConstants.RIGHT);
    jt6.setText("");
    jt6.setBorder(null);
    jt6.setFont(new java.awt.Font("Dialog", 1, 14));
    jt6.setBounds(new Rectangle(320, 223, 129, 23));
    jLabel9.setText("وصف الصنف");
    jLabel9.setHorizontalAlignment(SwingConstants.CENTER);
    jLabel9.setBorder(null);
    jLabel9.setForeground(Color.black);
    jLabel9.setFont(new java.awt.Font("Dialog", 1, 14));
    jLabel9.setBounds(new Rectangle(462, 153, 82, 26));
    jLabel11.setText("مكان التخزين");
    jLabel11.setHorizontalAlignment(SwingConstants.CENTER);
    jLabel11.setBorder(null);
    jLabel11.setForeground(Color.black);
    jLabel11.setFont(new java.awt.Font("Dialog", 1, 14));
    jLabel11.setBounds(new Rectangle(464, 187, 80, 27));
    jLabel8.setBounds(new Rectangle(466, 123, 73, 24));
    jLabel8.setFont(new java.awt.Font("Dialog", 1, 13));
    jLabel8.setText("الرصيد المتاح");
    jTItemBlanace1.setBounds(new Rectangle(354, 126, 95, 21));
    jTItemBlanace1.setText("");
    this.getContentPane().add(jLabel3, null);
    this.getContentPane().add(jComboMainGroups, null);
    this.getContentPane().add(jLabel4, null);
    this.getContentPane().add(jComboSubGroups, null);
    this.getContentPane().add(jComboItems, null);
    this.getContentPane().add(jTItemBlanace, null);
    this.getContentPane().add(jLabel5, null);
    this.getContentPane().add(jLabel6, null);
    this.getContentPane().add(jLabel9, null);
    this.getContentPane().add(jt9, null);
    this.getContentPane().add(jLabel11, null);
    this.getContentPane().add(jLabel7, null);
    this.getContentPane().add(jt10, null);
    this.getContentPane().add(jt6, null);
    this.getContentPane().add(jTItemBlanace1, null);
    this.getContentPane().add(jLabel8, null);
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
  Dimension frameSize = this.getSize();
  if (frameSize.height > screenSize.height) {
    frameSize.height = screenSize.height;
  }
  if (frameSize.width > screenSize.width) {
    frameSize.width = screenSize.width;
  }
  this.setLocation((screenSize.width - frameSize.width) / 2, (screenSize.height - frameSize.height) / 2);
  this.setVisible(true);
  this.setSize(new Dimension(616, 439));
  query="select * from MainGroups";
   try{
     con = DriverManager.getConnection(url, " ", "");
     stat = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
     rset = stat.executeQuery(query);
     int i=0;

     while(rset.next()) {
         String grname=rset.getString("GroupName").trim();
         this.jComboMainGroups.insertItemAt(grname,i );

         i++;
     }
     if(i>0)
       this.jComboMainGroups.setSelectedIndex(0);
   }
   catch(SQLException ex){
     JOptionPane.showMessageDialog(null,"فشل في الربط مع قاعدة البيانات"+ex.toString() );
   }
    jTItemBlanace.addActionListener(new Framereport_jTItemBlanace_actionAdapter(this));


 }

  void jComboMainGroups_itemStateChanged(ItemEvent e) {
    query="select * from MainGroups where GroupName='"+this.jComboMainGroups.getSelectedItem().toString().trim()+"'";
       try{
         con = DriverManager.getConnection(url, " ", "");
         stat = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
         rset = stat.executeQuery(query);
         if(rset.next()) {
            maingroupcode=Integer.parseInt(rset.getString("MainGroupCode").trim());
           query="select * from SubGroups where MainGroups="+maingroupcode;

         stat1 = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
           rset1 = stat1.executeQuery(query);
           int i=0;
           this.jComboSubGroups.removeAllItems();
           while(rset1.next()) {
             this.jComboSubGroups.insertItemAt(rset1.getString("SubGroupName").trim(),i );
             i++;
           }
            if(i>0)
              this.jComboSubGroups.setSelectedIndex(0);
         }
       }
       catch(SQLException ex){
         JOptionPane.showMessageDialog(null,"فشل في الربط مع قاعدة البيانات"+ex.toString() );
       }

    }
    void jComboSubGroups_itemStateChanged(ItemEvent e) {
      this.jComboItems.removeAllItems();
        query="select * from SubGroups where SubGroupName='"+this.jComboSubGroups.getSelectedItem().toString().trim()+"' and MainGroups="+maingroupcode;
       try{
        con = DriverManager.getConnection(url, " ", "");
        stat = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
        rset = stat.executeQuery(query);
        if(rset.next()) {
           subgroupcode=Integer.parseInt(rset.getString("SubGroupCode").trim());
          query="select * from Items where MainGroupCode="+maingroupcode+" and SupGroupCode="+subgroupcode;
          rset = stat.executeQuery(query);
          int i=0;
          while(rset.next()) {
            this.jComboItems.insertItemAt(rset.getString("ItemName").trim(),i );
            i++;
          }
         if(i>0)
             this.jComboItems.setSelectedIndex(0);

        }
       }
       catch(SQLException ex){
        JOptionPane.showMessageDialog(null,"فشل في الربط مع قاعدة البيانات"+ex.toString() );
       }

  }



  void jComboItems_itemStateChanged(ItemEvent e) {
    query="select * from Items where MainGroupCode="+maingroupcode+" and SupGroupCode="+subgroupcode +" and ItemName='"+this.jComboItems.getSelectedItem().toString().trim()+"'";
   try{
    con = DriverManager.getConnection(url, " ", "");
    stat = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
    rset = stat.executeQuery(query);
    if(rset.next()) {
       itemcode=Integer.parseInt(rset.getString("itemCode").trim());
       jTItemBlanace1.setText(rset.getString("ItemBlanace") );
       jt9.setText(rset.getString("ItemDesc"));
       jt6.setText(rset.getString("ItemType"));
       jTItemBlanace.setText(rset.getString("ItemPrice"));
       jt10.setText(rset.getString("ItemPalce"));
   }
    else{
      JOptionPane.showMessageDialog(null,"هذا الصنف غير مسجل له بيانات");
       }
   }
   catch(SQLException ex){
    JOptionPane.showMessageDialog(null,"فشل في الربط مع قاعدة البيانات"+ex.toString() );
   }

  }

  void jTItemBlanace_actionPerformed(ActionEvent e) {

  }



  }

class Framereport_jComboMainGroups_itemAdapter implements java.awt.event.ItemListener {
  Framereport adaptee;

  Framereport_jComboMainGroups_itemAdapter(Framereport adaptee) {
    this.adaptee = adaptee;
  }
  public void itemStateChanged(ItemEvent e) {
    adaptee.jComboMainGroups_itemStateChanged(e);
  }
}

class Framereport_jComboSubGroups_itemAdapter implements java.awt.event.ItemListener {
  Framereport adaptee;

  Framereport_jComboSubGroups_itemAdapter(Framereport adaptee) {
    this.adaptee = adaptee;
  }
  public void itemStateChanged(ItemEvent e) {
    adaptee.jComboSubGroups_itemStateChanged(e);
  }
}

class Framereport_jComboItems_itemAdapter implements java.awt.event.ItemListener {
  Framereport adaptee;

  Framereport_jComboItems_itemAdapter(Framereport adaptee) {
    this.adaptee = adaptee;
  }
  public void itemStateChanged(ItemEvent e) {
    adaptee.jComboItems_itemStateChanged(e);
  }
}

class Framereport_jTItemBlanace_actionAdapter implements java.awt.event.ActionListener {
  Framereport adaptee;

  Framereport_jTItemBlanace_actionAdapter(Framereport adaptee) {
    this.adaptee = adaptee;
  }
  public void actionPerformed(ActionEvent e) {
    adaptee.jTItemBlanace_actionPerformed(e);
  }
}