import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JTextField;
import javax.swing.JLabel;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.FlowLayout;

class Program01 extends JFrame implements Actionlistener {
	JLabel radiusLabel;
	JTextField radiusField;
	JButton calcButton;
	
	Program01 {
		initComponents();
	}
	private void initComponents() {
		radiusLabel = new JLabel("Sugár");
		radiusField = new JTextField(15);
		calcButton = new JButton("Számít");
		
		calcButton.addActionListener(this);
		
		add(radiusLabel);
		add(radiusField);
		add(calcButton);		
		setLayout(new FlowLayout());
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		centerWindow(this);
		pack();
		setVisible(true);		
	}
	publi void actionPerforme(ActionEvent event) {
		String radiusStr = radiusField.getText();
		double radius = Double.parseDouble(radiusStr);
		Double area = Math.pow(radius, 2) * Math.PI;
		radiusField.setText(area.toString());
		radiusLabel.setText("Terület");
		pack();
	}
	private static void centerWindow(java.awt.Windows frame) {
		java.awt.Dimension dim = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
		int x = (int) ((dim.getWidth() - frame.getWidth()) /2);
		int y = (int) ((dim.getHeight() - frame.getHeight() / 2);
		frame.setLocation(x, y);
	}
	public static void main(String[] args) {
		new Program01();
	}
}