how to do gui

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

public class ShippingCost {

public static void main(String[] args){

JFrame f=new JFrame();
JLabel lab1=new JLabel("Enter Item Name: ");
JLabel lab2=new JLabel("Enter Weight: ");
final JTextField text1=new JTextField(20);
final JTextField text2=new JTextField(20);
JPanel p=new JPanel(new GridLayout(3,2));
JButton b=new JButton("Find");

p.add(lab1);
p.add(text1);
p.add(lab2);
p.add(text2);
p.add(b);
b.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent e){
String itemName = text1.getText();
    double weight = Double.parseDouble(text2.getText());
    double firstKg = 10.0;
    double nextKg = 5.0;
    double num1 = 0.0;

    if(weight <= 1.0){
        System.out.println("Your shipping cost is RM" + firstKg );
    }else {
        weight = weight - 1;
        num1 = weight * nextKg;
        num1 = firstKg + num1;
        System.out.println("Your shipping cost is RM" + num1);
    }
    }
});
    f.add(p);
    f.setVisible(true);
    f.setSize(300,100);
    }
}

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

public class ShippingCost {

public static void main(String[] args){

JFrame f=new JFrame();
JLabel lab1=new JLabel("Enter Item Name: ");
JLabel lab2=new JLabel("Enter Weight: ");
final JTextField text1=new JTextField(20);
final JTextField text2=new JTextField(20);
JPanel p=new JPanel(new GridLayout(3,2));
JButton b=new JButton("Find");

p.add(lab1);
p.add(text1);
p.add(lab2);
p.add(text2);
p.add(b);
b.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent e){
String itemName = text1.getText();
    double weight = Double.parseDouble(text2.getText());
    double firstKg = 10.0;
    double nextKg = 5.0;
    double num1 = 0.0;

    if(weight <= 1.0){
        JOptionPane.showMessageDialog(null,"Your shipping cost is RM" + firstKg );
    }else {
        weight = weight - 1;
        num1 = weight * nextKg;
        num1 = firstKg + num1;
        JOptionPane.showMessageDialog(null,"Your shipping cost is RM" + num1);
    }
    }
});
    f.add(p);
    f.setVisible(true);
    f.setSize(300,100);
    }
}