How to check the value from user input in database or not?

Question

Hello;
I want to check the value of user input from JtextFiled in my database or not.
If it is in database, then i will pop up a window to tell us, otherwise, it will tell us it is not in database.
My problem is my code do not work properly, sometimes, it tell me correct information, sometime it tell wrong information.
Could anyone help,please.Thanks
The following code is for check whether the value in database or not, and pop up a window to tell us.
while( rs.next()) {
                System.out.println("i am testing");
                bInt=new Integer(rs.getInt("id"));
                if(aInt.equals(bInt)){ // If i find the value in data base, set flag to 1.
              flag=1;  //I set a flag to check whether the id in database or not
                    break;
         System.out.println("falg" + flag);
            if(flag==1){ //?????????????????????
          String remove1 = "DELETE FROM Rental WHERE CustomerID=" + a;
          String remove2 = "DELETE FROM Revenus WHERE CustomerID=" +a;
          String remove3 = "DELETE FROM Customer WHERE id=" +a;
          s.executeUpdate(remove1);
          s.executeUpdate(remove2);
          s.executeUpdate(remove3);
                JOptionPane.showMessageDialog(null,"you have success delete the value");
          s.close();
         else//???????????????????????????????
              JOptionPane.showMessageDialog(null,"I could not found the value"); -------------------------------------------------------------------
My whole program
import java.sql.*;
import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JOptionPane;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
public class DeleteC extends JFrame
    public static int index=0;   
    public static ResultSet rs;
    public static Statement s;
    public static Connection c;
    public static  Object cols[][];
    private static JTable table;
    private static JScrollPane scroller;
    private static int flag=0;
    public DeleteC()
        //information of our connection
        //the url of the database: protocol:subprotocol:subname:computer_name:port:database_name
        String strUrl      = "jdbc:oracle:thin:@augur.scms.waikato.ac.nz:1521:teaching";
        //user name and password
        String strUser      = "xbl1";
        String strPass      = "19681978";
        //try to load the driver
        try {
            Class.forName("oracle.jdbc.driver.OracleDriver");
        catch (ClassNotFoundException e) {
            System.out.println( "Cannot load the Oracle driver. Include it in your classpath.");
            System.exit( -1);
        //a null reference to a Connection object
        c = null;
        try {
            //open a connection to the database
            c = DriverManager.getConnection( strUrl, strUser, strPass);
        catch (SQLException e) {
            System.out.println("Cannot connect to the database. Here is the error:");
            e.printStackTrace();
            System.exit( -1);
       //create a statement object to execute sql statements
    public void getData(String a){
        try {
         //create a statement object to execute sql statements
         s = c.createStatement();
            int index=0;
            Integer aInt= Integer.valueOf(a);
            Integer bInt;
              //our example query
            String strQuery = "select id from customer";
            //execute the query
            ResultSet rs = s.executeQuery( strQuery);
            //while there are rows in the result set
            while( rs.next()) {
                System.out.println("i am testing");
                bInt=new Integer(rs.getInt("id"));
                if(aInt.equals(bInt)){
              //JOptionPane.showMessageDialog(null,"I found the value"); 
              flag=1;
                    break;
         System.out.println("falg" + flag);
            if(flag==1){
          String remove1 = "DELETE FROM Rental WHERE CustomerID=" + a;
          String remove2 = "DELETE FROM Revenus WHERE CustomerID=" +a;
          String remove3 = "DELETE FROM Customer WHERE id=" +a;
          s.executeUpdate(remove1);
          s.executeUpdate(remove2);
          s.executeUpdate(remove3);
                JOptionPane.showMessageDialog(null,"you have success delete the value");
          s.close();
         else
              JOptionPane.showMessageDialog(null,"I could not found the value");
        catch (SQLException e) {
             JOptionPane.showMessageDialog(null,"You may enter wrong id");
My main program for user input from JTextField.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.JOptionPane;
import java.util.*;
public class EnterID extends JFrame{
    public JTextField tF1;
    public EnterID enID;
    public String tF1Value;
    private JLabel label1, label2, label3;
    private static JButton button;
    private static ButtonHandler handler;
    private static String aString;
    private static Integer aInteger;
    private static Integer checkV=0;
    public static void main(String args[]){
       EnterID eId= new EnterID();
   public EnterID(){
      handler=new ButtonHandler();
      Container c= getContentPane();
      c.setLayout(new GridLayout(3,1));
      button= new JButton("ok");
      button.addActionListener(handler);
      label1 = new JLabel(" CustomerID, Please");
      label2 = new JLabel("Label2");
      label3 = new JLabel();
      label3.setLayout(new GridLayout(1,1));
      label3.add(button);
      label2.setLayout(new GridLayout(1,1));
      aString = "Enter Id Here";
      tF1 = new JTextField(aString);
      label2.add(tF1);
      c.add(label1);
      c.add(label2);         
      c.add(label3);            
      setSize(150,100);
      setVisible(true);     
   private class ButtonHandler implements ActionListener{
     public void actionPerformed(ActionEvent event){
         tF1Value=tF1.getText();
        //   CheckData cData = new CheckData();
         //  aInteger = Integer.valueOf(tF1Value);      
         if(tF1Value.equals(aString)){
          JOptionPane.showMessageDialog(null,"You didn't type value into box");
          setVisible(false); 
        else {
            DeleteC dC= new DeleteC();
            dC.getData(tF1Value);
            setVisible(false); 
}

Answer 1

You may have working code now, but the code you posted is horrible and I'm going to tell you a much much much better approach for the JDBC part. (You should probably isolate your database code from your user interface code as well, but I'm skipping over that structural problem...)
Do this instead:
    public void getData(String a){
        PreparedStatement p;
        String strQuery = "select count(*) the_count from customer where id = ?";
        try {   
         //create a prepared statement object to execute sql statements, it's better, faster, safer
         p = c.prepareStatement(strQuery);
            // bind the parameter value to the "?"
            p.setInt(1, Integer.parseInt(a) );
            //execute the query
            ResultSet rs = p.executeQuery( );
            // if the query doesn't throw an exception, it will have exactly one row
            rs.next();
            System.out.println("i am testing");
            if (rs.getInt("the_count") > 0 ) {
            // it's there, do what you need to...
         else
              JOptionPane.showMessageDialog(null,"I could not find the value");
        catch (SQLException e) {
             // JOptionPane.showMessageDialog(null,"You may enter wrong id");
             // if you get an exception, something is really wrong, and it's NOT user error
        // always, always, ALWAYS close JDBC resources in a finally block
        finally
            p.close();
    }First, this is simpler and easier to read.
Second, this retrieves just the needed information, whether or not the id is in the database. Your way will get much much slower as more data goes into the database. My way, if there is an index on the id column, more data doesn;t slow it down very much.
I've also left some important points in comments.
No guarantees that there isn't a dumb typo in there; I didn't actually compile it, much less test it. It's at least close though...