import java.awt.*;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.*;

public class Set6_GUIUnits {

public static void main(String[] args) {

JFrame frame = new JFrame();

frame.setLayout(new BorderLayout());

JLabel label_no_of_units = new JLabel("Number of Units:");

JTextField textfield_units = new JTextField();

JLabel label_billamount = new JLabel("Bill Amount");

JButton btn_calculate_bill = new JButton("Calculate Bill");

JPanel top_panel = new JPanel();

JPanel center_panel = new JPanel();

JPanel bottom_panel = new JPanel();

top_panel.setLayout(new GridLayout(2, 1));

center_panel.setLayout(new FlowLayout(0, 0, 200));

top_panel.add(label_no_of_units);

top_panel.add(textfield_units);

center_panel.add(label_billamount);

bottom_panel.add(btn_calculate_bill);

frame.add(top_panel, BorderLayout.NORTH);

frame.add(center_panel, BorderLayout.CENTER);

frame.add(bottom_panel, BorderLayout.SOUTH);

frame.setSize(500, 500);

frame.setTitle("Bill-Calculator!!");

frame.setVisible(true);

btn_calculate_bill.addActionListener(new ActionListener() {

@Override

public void actionPerformed(ActionEvent e) {

String user_input = textfield_units.getText();

int bill = calculateBill(Integer.parseInt(user_input));

label_billamount.setText("Unit Consumption : " + user_input + " Bill : " + bill);

throw new UnsupportedOperationException("Unimplemented method 'actionPerformed'");

}

});

}

public static int calculateBill(int units) {

int charge = 1;

if (units <= 200) {

charge = 3;

} else if (units > 200 && units < 300) {

charge = 4;

} else {

charge = 5;

}

return units * charge;

}

}