Inner not knowing about outer

[Al Wells]

I have, through the kind help of some of the people here, figured out some of my problems in learning swing. But, now, I am having trouble with getting an inner class to see objects in the outer class. What is wrong with my syntax that is causing this? Thanks in advance for your help.

 
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
 

public class TestMainScreen extends JFrame  {

public static void main (String [] args) {

new TestMainScreen();

}

public TestMainScreen(){

this.setTitle("SM O2 Rounds");
this.setSize(500, 500);
this.setDefaultCloseOperation(EXIT_ON_CLOSE);

JPanel mainPanel = new JPanel();

JLabel uNameLabel = new JLabel("Enter your user name: ");
JTextField uNameField = new JTextField(20);
JLabel pWordLabel = new JLabel("Enter your password: ");
JTextField pWordField = new JTextField(20);

JButton mainButton = new JButton("Login");
MainButtonListener mbl = new MainButtonListener();
mainButton.addActionListener(mbl);

mainPanel.add(uNameLabel);
mainPanel.add(uNameField);
mainPanel.add(pWordLabel);
mainPanel.add(pWordField);
mainPanel.add(mainButton);

this.add(mainPanel);
this.setLocationRelativeTo(null);
this.setVisible(true);

}

private class MainButtonListener implements ActionListener {
public void actionPerformed (ActionEvent e) {

if(e.getSource() == mainButton)//does not see mb {
String uNameString = uNameField.getText();
String pWordString = pWordField.getText();

if (uNameString.length()== 0 || pWordString.length() == 0){
JOptionPane.showMessageDialog (TestMainScreen.this, "You must enter a user name and password.", JOptionPane.INFORMATION_MESSAGE);

}//Close inner if
else { //Will be a log in object created here if I can get the rest of this working
JOptionPane.showMessageDialog(TestMainScreen.this, "Logging you in.", JOptionPane.INFORMATION_MESSAGE);
}//Close else
}//close outer if
}//close method
}//close inner class
}//close class
 

[Gregg Bolinger]

It's because you've defined mainButton inside the constructor instead of defining it globally for the class. So it is only visible in the TestMainScreen constructor method.

[Ernest Friedman-Hill]

mainButton is a local variable declared in the constructor of the outer class. Local variables are only visible inside the method that declares them. If you want MainButtonListener to see it, make it into a member variable of the class -- i.e., declare it at class scope, and then assign it in the constructor as now.

public class TestMainScreen extends JFrame  {
    JButton mainButton;
    ...
    public TestMainScreen(){
        ...
        mainButton = new JButton("Login");

[Gregg Bolinger]

With that being said, several of your variables are going to have the same issue because they are in declared in the constructor.

uNameField
pWordField

Will both need to be made global to the class.

[Al Wells]

Then this should do the trick?

 
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class TestMainScreen extends JFrame  {

public static void main (String [] args) {

new TestMainScreen();

}

private JButton mainButton;
private JTextField uNameField;
private JTextField pWordField;

public TestMainScreen(){ //rest of code...
 

Thanks Greg and Ernest!
[ May 23, 2005: Message edited by: Al Wells ]

[Gregg Bolinger]

Originally posted by Al Wells:
Then this should do the trick?

 
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
 
 
public class TestMainScreen extends JFrame  {

public static void main (String [] args) {

new TestMainScreen();

}

private JButton mainButton;
private JTextField uNameField;
private JTextField pWordField;

public TestMainScreen(){ //rest of code...
 

Thanks Greg.

Yep, that should pretty much do it. Note also that your JOptionPane.showMessageDialog argumaents are missing the Dialog Title.

JOptionPane.showMessageDialog(TestMainScreen.this, 
                              "Logging you in.", 
                              "Login", 
                              JOptionPane.INFORMATION_MESSAGE);

[Al Wells]

I noticed that when I just compiled. I am fixing now.