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

public class Sqrt2 extends JFrame {
    private JLabel label = new JLabel("Här visas roten");
    private JTextField text = new JTextField("Skriv talet här");
    private JButton button = new JButton("Visa rot!");
    private ButtonListener bl = new ButtonListener();

    public Sqrt2() {
	super("Sqrt2");
        button.addActionListener(bl);
        Container cp = getContentPane();
        cp.setLayout(new FlowLayout());
        cp.add(text);
        cp.add(button);
        cp.add(label);
    }

    // Inre klass för att lyssna på knapp
    class ButtonListener implements ActionListener {

        // Hantera klick på roten-ur-knapp
        public void actionPerformed(ActionEvent event) {
            String numbuf = text.getText();
            try {
                float num = Float.parseFloat(numbuf);
                float res = (float)Math.sqrt(num);
                if (Float.isNaN(res))
                    label.setText("Det måste vara ett positivt tal.");
                else
                    label.setText("Roten ur " + num + " är " + res);
            }
            catch (NumberFormatException exc) {
                label.setText("'" + numbuf + "' är inte ett tal.");
            }
        } // actionPerformed
    } // class ButtonListener

    public static void main(String[] args) {

	String laf = UIManager.getSystemLookAndFeelClassName();
	try {
	    UIManager.setLookAndFeel(laf);
	    // If you want the Cross Platform L&F instead, replace
	    // UIManager.getSystemLookAndFeelClassName()
	    // with
	    // UIManager.getCrossPlatformLookAndFeelClassName()
	} catch (UnsupportedLookAndFeelException exc) {
	    System.err.println("Warning: UnsupportedLookAndFeel: " + laf);
	} catch (Exception exc) {
	    System.err.println("Error loading " + laf + ": " + exc);
	}

        Sqrt2 frame = new Sqrt2();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(200, 100);
        frame.setVisible(true);
    }
} // class Sqrt2