how to enhance code from extension class file using constructor

[Jhovarie]

hello guys is there another way to improve this code from extension class using constructor?

new Main_extension(usrnm,pwd,btn);

the code above is working but i want to access usrnm,pwd and btn
using "new Main_extension();" not "new Main_extension(usrnm,pwd,btn);"
is there another way to do that? thanks...

Full Code Main.java and Main_extension.java

Main.java

import javax.swing.*;
public class Main extends JFrame{ 
 private JTextField usrnm;
 private JPasswordField pwd;
 private JButton btn;
  public Main(){
   usrnm = new JTextField(10);
   pwd = new JPasswordField("mypassword",10);
   btn = new JButton("Login");
   add(usrnm);
   add(pwd);
   add(btn);
 
   new Main_extension(usrnm,pwd,btn); //<-- this work find
 
   setLayout(new java.awt.FlowLayout());
   setBounds(10,10,400,300);
   setDefaultCloseOperation(EXIT_ON_CLOSE);
   setVisible(true);
 }
 public static void main(String[]args){
   new Main();
 }
}

Main_extension.java

import javax.swing.*;
import java.awt.event.*;
public class Main_extension{
 public Main_extension(final JTextField usrnm,final JPasswordField pwd,JButton btn){
  btn.addActionListener(new ActionListener(){
   public void actionPerformed(ActionEvent evt){
    System.out.println("UserName: "+usrnm.getText());
	System.out.println("Password: "+pwd.getText());
   }
  });
 }
}

[sunde887]

Write a default constructor.

Some things to remember;
The compiler will provide a default constructor if you don't supply one which sets all objects to null, booleans to false, and numbers to 0 or 0.0

If one constructor is provided the compiler will no longer provide the above default constructor and you will be responsible for writing it if you want it.

Also, getting a reference to the object may be helpful.

[Jhovarie]

Write a default constructor.

Some things to remember;
The compiler will provide a default constructor if you don't supply one which sets all objects to null, booleans to false, and numbers to 0 or 0.0

If one constructor is provided the compiler will no longer provide the above default constructor and you will be responsible for writing it if you want it.

Also, getting a reference to the object may be helpful.

"getting a reference to the object may be helpful" by using static variable right?

[sunde887]

No, static variables should be avoided except for special cases. Rather than doing

new ClassName();

Do

ClassName varName = new ClassName();

[Jhovarie]

by using ClassName varName = new ClassName(); we must use some method right?