Stop a method from executing until another class does its bit

Question

Hi all,
For my app I have a login screen where to get login success the user must first register. I therefore have two class LoginDialog and Register which is a dialog.
In LoginDialog if the user clicks on Register it brings up a new instance of the Register dialog but continues to process the calling method (which happens to return to another class processing the login). What I require is that when I create a new Register object, the creating method does nothing until the Registration form is completed. I'm not at all au fait with threads so was wondering if there is an easy way to do it.
I have thought of passing the LoginDialog as an argument in the Register constructor and having an empty while loop running in the invoking method (i.e. while (false) do nothing) and creating public access to that boolean variable so that at completion of the registration it sets the boolean variable to true in LoginDialog so it should break out of the while loop and continue. Is that a satisfactory way of pausing and restarting a method?
Cheers,
Chris

Answer 1

Hi,
I have a MainFrame class which calls processLogin which creates a new LoginDialog which houses the Register button. When I click on the register button it opens a new Registration screen but LoginDialog returns to MainFrame in the background and says that no user has logged in. What I require is that when the Register object is created after clicking the Register button that LoginDialog waits until the Registration is complete.
Maybie the code will help (sorry if it is a bit lengthy).
Snippet of LoginDialog
public void actionPerformed(ActionEvent event)
        if(event.getSource() == ok) {
             _username = user.getText();
               _password = new String(password.getPassword());
               _server = server.getText();
               //ensure port number is an integer
               try{
                    _port = Integer.parseInt(port.getText());
               catch(NumberFormatException e){
                    JOptionPane.showMessageDialog(this,
                    "Please use an integer value only for the port number","Error",
                    JOptionPane.WARNING_MESSAGE);
               //checks username and password length
               if((_username.length()==0) || (_password.length() == 0)){
                    JOptionPane.showMessageDialog(this,
                         "Please enter a valid username and password","Error",
                              JOptionPane.WARNING_MESSAGE);
                    return;
               //checks server length
               if(_server.length()== 0){
                    JOptionPane.showMessageDialog(this,
                         "Invalid server host","Error",
                              JOptionPane.WARNING_MESSAGE);
                    return;
               try{
                    db = new DatabaseConnection();
                    boolean exists = db.doesUserExist(_username, _password);
                    db.close();
                    if(exists){
                         //System.out.println("User exists on database");
                         this.dispose(); //get rid of login screen now user is confirmed
                    if(!exists){
                              _username = null;
                              _password = null;
                              this.dispose();
               catch(java.sql.SQLException e){
                    JOptionPane.showMessageDialog(this,
                         "Unable to connect to database. Please try again.","Error",
                              JOptionPane.WARNING_MESSAGE);
          else if(event.getSource() == cancel) {
               //NOTHING
          else if(event.getSource() == register){
               Register register = new Register();
               //while (processRegistration){
          this.setVisible(false);
     }and Register
//import classes
import java.io.*;
import java.net.*;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.util.*;
public class Register extends JFrame implements ActionListener {
     //declare components
     JLabel lblHeading;
     JLabel lblUserName;
     JLabel lblUserPwd;
     JLabel lblCnfUserPwd;
     JLabel lblFirstName;
     JLabel lblLastName;
     JLabel lblAge;
     JLabel lblEmpId;
     JLabel lblEmail;
     JLabel lblSex;
     String userName;
     char[] userPwd;
     char[] cnfPwd;
     String strUserPwd;
     String strCnfUserPwd;
     String firstName;
     String lastName;
     String age;
     String empid;
     String email;
     String sexStr;
     Socket toServer;
     ObjectInputStream streamFromServer;
     PrintStream streamToServer;
     JComboBox comboSex;
     JTextField txtUserName;
     JPasswordField txtUserPwd;
     JPasswordField txtCnfUserPwd;
     JTextField txtFirstName;
     JTextField txtLastName;
     JTextField txtAge;
     JTextField txtEmpId;
     JTextField txtEmail;
     Font f;
     Color r;
     JButton btnSubmit;
     JButton btnCancel;
     DatabaseConnection db;
     boolean exists, entrySuccess;
     public Register() {
          this.setTitle("Register");
        JPanel panel=new JPanel();
          //apply the layout
           panel.setLayout(new GridBagLayout());
           GridBagConstraints gbCons=new GridBagConstraints();
          //place the components
          gbCons.gridx=0;
          gbCons.gridy=0;
          lblHeading=new JLabel("Registration Info");
           Font f = new Font("Monospaced" , Font.BOLD , 12);
          lblHeading.setFont(f);
          Color c=new Color(0,200,0);
          lblHeading.setForeground(new Color(131,25,38));
          lblHeading.setVerticalAlignment(SwingConstants.TOP);
          gbCons.anchor=GridBagConstraints.EAST;
          panel.add(lblHeading, gbCons);
          gbCons.gridx = 0;
          gbCons.gridy = 1;
          lblUserName = new JLabel("Enter Username");
          gbCons.anchor=GridBagConstraints.WEST;
          panel.add(lblUserName, gbCons);
          gbCons.gridx=1;
          gbCons.gridy=1;
          txtUserName=new JTextField(15);
          panel.add(txtUserName, gbCons);
          gbCons.gridx=0;
          gbCons.gridy=2;
          lblUserPwd=new JLabel("Enter Password ");
          panel.add(lblUserPwd, gbCons);
          gbCons.gridx = 1;
          gbCons.gridy = 2;
          txtUserPwd = new JPasswordField(15);
          panel.add(txtUserPwd, gbCons);
          gbCons.gridx=0;
          gbCons.gridy=3;
          lblCnfUserPwd=new JLabel("Confirm Password ");
          panel.add(lblCnfUserPwd, gbCons);
          gbCons.gridx=1;
          gbCons.gridy=3;
          txtCnfUserPwd=new JPasswordField(15);
          panel.add(txtCnfUserPwd, gbCons);
          gbCons.gridx=0;
          gbCons.gridy=4;
          lblEmpId=new JLabel("Employee ID");
          panel.add(lblEmpId, gbCons);
          gbCons.gridx=1;
          gbCons.gridy=4;
          txtEmpId=new JTextField(15);
          panel.add(txtEmpId, gbCons);
          gbCons.gridx=0;
          gbCons.gridy=5;
          lblFirstName=new JLabel("First Name");
          panel.add(lblFirstName, gbCons);
          gbCons.gridx=1;
          gbCons.gridy=5;
          txtFirstName=new JTextField(15);
          panel.add(txtFirstName, gbCons);
          gbCons.gridx=0;
          gbCons.gridy=6;
          lblLastName=new JLabel("Last Name");
          panel.add(lblLastName, gbCons);
          gbCons.gridx = 1;
          gbCons.gridy = 6;
          txtLastName=new JTextField(15);
          panel.add(txtLastName, gbCons);
          gbCons.gridx=0;
          gbCons.gridy=7;
          lblAge=new JLabel("Age");
          panel.add(lblAge, gbCons);
          gbCons.gridx=1;
          gbCons.gridy=7;
          txtAge=new JTextField(3);
          panel.add(txtAge, gbCons);
          gbCons.gridx=0;
          gbCons.gridy=8;
          lblEmail=new JLabel("Email");
          panel.add(lblEmail, gbCons);
          gbCons.gridx=1;
          gbCons.gridy=8;
          txtEmail=new JTextField(20);
          panel.add(txtEmail, gbCons);
          gbCons.gridx=0;
          gbCons.gridy=9;
          lblSex=new JLabel("Sex");
          panel.add(lblSex, gbCons);
          gbCons.gridx = 1;
          gbCons.gridy=9;
          String [] sexArr = {"Male", "Female"};
          comboSex = new JComboBox(sexArr);
          comboSex.setSelectedIndex(0);
          panel.add(comboSex, gbCons);
          JPanel btnPanel=new JPanel();
          btnSubmit=new JButton("Submit");
          btnPanel.add(btnSubmit);
          btnSubmit.addActionListener(this); //add listener to the Submit button
          btnCancel=new JButton("Cancel");
          btnPanel.add(btnCancel);
          btnCancel.addActionListener(this); //add listener to the Cancel button
          gbCons.gridx=0;
          gbCons.gridy=10;
          gbCons.anchor=GridBagConstraints.EAST;
          panel.add(btnPanel, gbCons);
          getContentPane().add(panel);
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
          setVisible(true);
          setSize(450,400);
     }//end or Register()
     public void actionPerformed(ActionEvent ae) {
          Object o = ae.getSource(); //get the source of the event
          if(o == btnCancel)
               this.dispose();
          if(o == btnSubmit){
               userName = txtUserName.getText();
               userPwd = txtUserPwd.getPassword();
               strUserPwd = new String(userPwd);
               cnfPwd = txtCnfUserPwd.getPassword();
               strCnfUserPwd = new String(cnfPwd);
               firstName = txtFirstName.getText();
               lastName = txtLastName.getText();
               age = txtAge.getText();
               empid = txtEmpId.getText();
               email = txtEmail.getText();
               sexStr = (String)comboSex.getItemAt(0);
               db = new DatabaseConnection();
               //Now check to see if username and password combination have been
               //taken
               try{
                    exists = db.doesUserExist(userName.trim(), strUserPwd.trim());
               catch (java.sql.SQLException e){
                    System.out.println(e);
               //Checks that each field has been filled in.
               if(userName.length() == 0 ||  strUserPwd.length() == 0 ||
               strCnfUserPwd.length() == 0 || firstName.length() == 0 ||
               lastName.length() == 0 || age.length() == 0 || empid.length() == 0
               || email.length() == 0){
                    JOptionPane.showMessageDialog(this,
                    "One or more entry has not been filled in. Please go back and try again",
                    "Message", JOptionPane.ERROR_MESSAGE);     
               //Ensures that passwords match
               if(!strUserPwd.equals(strCnfUserPwd)){
                    JOptionPane.showMessageDialog(this,
                    "Passwords do not match. Please go back and try again",
                    "Message", JOptionPane.ERROR_MESSAGE);
               if(exists){
                    JOptionPane.showMessageDialog(this,
                    "Username and password combination already exists. Please go back and try again",
                    "Message", JOptionPane.ERROR_MESSAGE);
               if(!exists) {
                    String userDetails = (userName.trim() + " " + strUserPwd.trim()
                    + " "  + firstName.trim() + " "
                    + lastName.trim() + " " + age.trim() + " " + empid.trim() + " "
                    + email.trim() + " " + sexStr.trim());
                    //System.out.println(userDetails);
                    //Try to connect to the database and insert the user details.
                    //If successful then user will be alerted and the registration page
                    //should be disposed automatically. If for some reason the insert
                    //was not successful then user is prompted to try again.
                    try{
                         entrySuccess = db.registerUser(userDetails);
                         if(entrySuccess){
                              JOptionPane.showMessageDialog(this,
                              "Congratulations, you have successfully registered for the Instant Messenger service!",
                              "Message", JOptionPane.INFORMATION_MESSAGE);
                              this.dispose();     
                         if(!entrySuccess){
                              JOptionPane.showMessageDialog(this,
                              "There was a problem entering your details. Please try again.",
                              "Message", JOptionPane.ERROR_MESSAGE);
                    catch(java.sql.SQLException e){
          }//end of else
          db.close();
     }//end of actionPerformed()
}//end of classCheers,
Chris