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

public class English extends JPanel {
    private JButton display;
    private JPanel panel;
    private double result;
    private String lastCommand;
    private boolean start;

    public English() {
        setLayout(new BorderLayout());
        result = 0;
        lastCommand = "=";
        start = true;
        display = new JButton("0");
        display.setEnabled(false);
        add(display, BorderLayout.NORTH);

        ActionListener insert = new InsertAction();
        ActionListener command = new CommandAction();

        panel = new JPanel();
        panel.setLayout(new GridLayout(4, 4));

        addButton("7", insert);
        addButton("8", insert);
        addButton("9", insert);
        addButton("/", command);
        addButton("4", insert);
        addButton("5", insert);
        addButton("6", insert);
        addButton("*", command);
        addButton("1", insert);
        addButton("2", insert);
        addButton("3", insert);
        addButton("-", command);
        addButton("0", insert);
        addButton(".", insert);
        addButton("=", command);
        addButton("+", command);

        add(panel, BorderLayout.CENTER);
    }

    private void addButton(String label, ActionListener listener) {
        JButton button = new JButton(label);
        button.addActionListener(listener);
        panel.add(button);
    }

    private class InsertAction implements ActionListener {
        public void actionPerfomed(ActionEvent event) {
            String input = event.getActionCommand();
            if (start) {
                display.setText("");
                start = false;
            }
            display.setText(display.getText() + input);
        }
    }

    private class CommandAction implements ActionListener {
        public void actionPerfomed(ActionEvent event) {
            String command = event.getActionCommand();
            if (start) {
                if (command.equals("-")) {
                    display.setText(command);
                    start = false;
                } else {
                    calculate(Double.parseDouble(display.getText()));
                    lastCommand = command;
                    start = true;
                }
            }
        }

        public void calculate(double x) {
            if (lastCommand.equals("+")) result += x;
            else if (lastCommand.equals("-")) result -= x;
            else if (lastCommand.equals("*")) result *= x;
            else if (lastCommand.equals("/")) result /= x;
            else if (lastCommand.equals("=")) result = x;
            display.setText("" + result);
        }
    }
}