Question

First post for me. I’m a student in my first year of a comp science degree.

I was just building a basic GUI for an assignment and for some reason, which I cannot see for the life of me, one of the JFrames I have created, an instance of the Register Class displays completely blank when it is called from the Register buttons action listener in the Login Class…

I also have an individual main Class which contains the Main method and calls the Login Class. The Login Class JFrame works fine and as mentioned, the issues only occur with the Registration Class when it is called within the Login Class’ Register button action listener. All other JFrames in the program work fine too.

I have attempted to call the Register Class direct from the main and it has the same issues, although I have attempted to reduce it to its most basic form and it still does not display anything aside from a blank uncolored JFrame.

Here is the code (Unfinished but working as is). I apologise for my sloppyness but I am a complete beginner.

Can anyone see what is wrong with it?

Thanks in advance!

    package guitest;

    import java.awt.Color;
    import java.awt.Component;
    import java.awt.FlowLayout;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import java.io.BufferedWriter;
    import java.io.FileWriter;
    import java.awt.event.*;
    import java.io.*;
    import javax.swing.*;

    public class Register extends JFrame{

        JButton regSubmit = new JButton("Submit");

        JTextField email = new JTextField();
        JTextField name = new JTextField();
        JTextField Address1 = new JTextField();
        JTextField Address2 = new JTextField();

        JPasswordField password1 = new JPasswordField();
        JPasswordField password2 = new JPasswordField();

        String nameTxt = email.getText();
        String passTxt = password1.getText();
        String info = "";

        FlowLayout layout1 = new FlowLayout();    

        public void Reg(){
            this.setTitle("La Volpe Registration");
            this.setLayout(layout1);    
            this.add(Address1);
            this.add(Address2);
            this.add(email);
            this.add(password1);
            this.add(password2);
            this.add(name);
            this.add(regSubmit);
            this.getContentPane().setBackground(Color.green);
            this.setSize(370, 160);

            regSubmit.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    regSubmitActionPerformed(evt);
                }

                private void regSubmitActionPerformed(java.awt.event.ActionEvent evt) { 

                String name = email.getText();
                String pass = password1.getText();
                String info = "";

                System.out.println("registering...");

                boolean eof;

                try{
                    // Create file
                    FileWriter file = new FileWriter("\\regdata.txt");
                    BufferedWriter out = new BufferedWriter(file);
                    out.write("\n"+nameTxt+", "+passTxt);
                }

                catch (Exception e){
                }   
            }   
        });
        this.setVisible(true);
    }    
}

---

And the class that links to it…

---

package guitest;

    import java.awt.Color;
    import java.awt.Component;
    import java.awt.FlowLayout;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import java.io.BufferedWriter;
    import java.io.FileWriter;
    import java.awt.event.*;
    import java.io.*;
    import javax.swing.*;

    /**
    * @author david
    */

    public class Login {

    JFrame loginFrame = new JFrame();
    Register reg3 = new Register();

    JButton submit = new JButton("Submit");
    JButton clear = new JButton("Clear");
    JButton register = new JButton ("Register with Us");

    JPasswordField pass = new JPasswordField(20);
    JTextField email = new JTextField(20);
    JLabel em = new JLabel("Email Address: ");
    JLabel pw = new JLabel("Password: ");

    String pathname;
    String line;
    String [] records = new String [1000];
    int count = 0;

    FlowLayout layout1 = new FlowLayout();

        public Login(){

            //Adds Email label and text field
            loginFrame.add(em);
            loginFrame.add(email);

            //Adds password label and field
            loginFrame.add(pw);
            loginFrame.add(pass);

            //Adds buttons
            loginFrame.add(submit);
            loginFrame.add(clear);
            loginFrame.add(register);

            loginFrame.getContentPane().setBackground(Color.green);

            loginFrame.setLayout(layout1);

            loginFrame.setSize(370, 160);

            loginFrame.setTitle("La Volpe - Login");

            submit.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    submitActionPerformed(evt);    
                }            

                private void submitActionPerformed(java.awt.event.ActionEvent evt){                                         
                String emailadd = email.getText();
                String password = pass.getText();
                pathname = "\\regdata.txt";

                boolean eof;

                try{
                    FileReader file = new FileReader(pathname);
                    BufferedReader buff = new BufferedReader(file);

                    eof = false; // set the eof boolean to false

                        while (!eof){
                        line = buff.readLine();
                        if (line == null){ // test to see if the end of file has been reached
                        eof = true;  // if the end of file has been found set the eof Boolean to true
                        }
                        else{ 
                        // end of file not reached so move the contents of the line to the records
                        //array
                        records[count] = line;
                        count ++;
                        System.out.println(line);  // print out the new line input for error checking
                        }
                    }    
                    buff.close();
                }
                catch (IOException e){
                    System.out.println("Error --  "+ e.toString());
                }

                boolean notTrue = false;

                for (int i = 0; i < count; i++) {       
                    if ((!notTrue)&&((emailadd + "," + password).equals(records[i]))) {
                        FoodSelectionMain loggedIn = new FoodSelectionMain();
                        loggedIn.setVisible(true);
                    } 
                }
                if (!notTrue){
                    JOptionPane.showInputDialog("Please check your login "
                    + "and try again. If you are a new user, please "
                    + "register by pressing the 'REGISTER' button");
                }
            }   

        }); 

        // TODO add your handling code here:


        clear.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                clearActionPerformed(evt);
            }

            public void clearActionPerformed(java.awt.event.ActionEvent evt){
                email.setText(null);
                pass.setText(null);
            }

        }); 
        register.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                registerActionPerformed(evt);
            }

            public void registerActionPerformed(java.awt.event.ActionEvent evt){
                reg3.setVisible(true);
                    System.out.println("Register pressed");
            }
        });
        loginFrame.setVisible(true);
    }
}

Answer 1

Try this,
in Register class, correct the constructor name to Register() from Reg().

Keep these few Guidelines in your mind before constructing a gui app

1. Create an object of the subclass of the container .

2. Consider all the components which goes in the container as instance variables.

3. Set these instance variable and event handling outside the constructor in methods, (ie setComponent(), setHandler().etc) but do these method invocations from constructor.

4. Now in main use this…

.

EventQueue.invokeLater(new Runnable() {

    public void run() {
        Myframe f = new Myframe();
        f.setVisible(true);
    }
}