import javax.swing.*;
import java.awt.*;
import java.util.Timer;
import java.util.*;

class React {
    private static Date startTime;

    public static void start() {
        startTime = new Date();
    }

    public static Long end() {
        return (new Date()).getTime() - startTime.getTime();
    }
}

class MyJFrame extends JFrame {
    private static Timer timer = new Timer();

    public MyJFrame(String title) {
        super(title);
        setSize(new Dimension(300, 150));
        setVisible(true);
        setLocationRelativeTo(null);
        setResizable(false);
        setLayout(GridBagLayout());
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        getContentPane().setBackground(Color.WHITE);

        JButton reactBtn = new JButton("Start");
        reactBtn.setFocusable(false);
        reactBtn.addActionListener(event => {
            if (reactBtn.getText().equalsIgnoreCase("start")) {
                reactBtn.setText("React");
                reactBtn.setEnabled(false);

                Random rand = new Random();
                scheduleTask(() -> {
                    getContentPane().setBackground(Color.BLUE);
                    React.start();
                    reactBtn.setEnabled(true);
                }, rand.nextInt(11500));

            } else {
                JOptionPane.showMessageDialog(null, "WINNER: " + React.end() + " milliseconds", "RESULT", JOptionPane.INFORMATION_MESSAGE);
                getContentPane().setBackground(Color.WHITE);
                reactBtn.setText("Start");
            }
        };

        add(reactBtn, new GridBagConstraints());
    }

    private void scheduleTask(final Runnable runnable, long delay) {
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                runnable.run();
            }
        }, delay);
    }

}

public class Debug {
    public static void main(String[] args) {
        new MyJFrame("React Play");
    }
}