Uso de StringBuffer. reverse (invertir strings).

Codigo:

1. import javax.swing.*;
2. import java.awt.*;
3. import java.awt.event.*;
4. public class Main extends JFrame {
5. .FlowLayout v = new FlowLayout();
6. .JButton boton1 = new JButton(" Revertir ");
7. .TextArea text = new TextArea("", 3, 30, 3);//row,col,nullScroll
8. .public Main() {
9. ...text.setText("Hola mundo");
10. ...add(text);
11. ...add(boton1);
12. ...getContentPane().setLayout(v);
13. ...setDefaultCloseOperation(EXIT_ON_CLOSE);
14. ...setSize(300,150);
15. ...setVisible(true);
16. //Event al pulsar boton
17. ...boton1.addActionListener (new ActionListener(){
18. ....public void actionPerformed(ActionEvent e){
19. .....StringBuffer str1 = new StringBuffer(text.getText());
20. ........text.setText(str1.reverse().toString());
21. ......}
22. ....});
23. ..}
24. ..public static void main(String[] args) { new Main(); }
25. }

Resultado: