How to make a java GUI

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

public class methodname extends JFrame
{
private JButton button = new JButton("Button");
private JTextField number;
private Double random;

public methodname() throws NullPointerException
{
Container pane = getContentPane();
pane.setLayout(new GridLayout(1,2));
number = new JTextField(1);
buttonHandler btHandler = new buttonHandler();
button.addActionListener(btHandler);
pane.add(button);
pane.add(number);
setSize(200,50);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}


private class buttonHandler implements ActionListener
{
public void actionPerformed(ActionEvent e) throws NullPointerException
{
random = Double.parseDouble(number.getText());
}
}
 public static void main(String[] args) throws NullPointerException
    {
     methodname whatever = new methodname();
    }
}

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

public class methodname extends JFrame
{
private JButton button = new JButton("Ok");
private JTextField number = new JTextField(1);
private JRadioButton radio = new JRadioButton();
private JLabel label = new JLabel("Base");
private String random;



public methodname() throws NullPointerException
{
setLayout(new GridLayout(2,2));


buttonHandler btHandler = new buttonHandler();
button.addActionListener(btHandler);

add(button);
add(number);
add(radio);
add(label);

setSize(200,75);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}


private class buttonHandler implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
random = number.getText();
System.out.println(random);
}
}
 public static void main(String[] args)
    {
     methodname whatever = new methodname();
    }
}