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

public class App extends JFrame implements ActionListener {
    public static void main(String args[]) {
        App j = new App();
	
    }

    public App() {
        this.getContentPane().setLayout(new FlowLayout());
        button  = new JButton("Hello");
        button.addActionListener(this);
        this.getContentPane().add(button);
	
	label = new JLabel();
	this.getContentPane().add(label);


	this.pack();
	this.setVisible(true);
	this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void actionPerformed(ActionEvent e) {

        if (e.getSource() == button) {
            label.setText("World");
            this.pack();
        }
    }
	JButton button;
	JLabel label;
}