Java - seleccionar texto de un jtextfield

public class FullSelectorListener extends java.awt.event.FocusAdapter {

    public FullSelectorListener() {

    }

    @Override

    public void focusLost(java.awt.event.FocusEvent evt) {

    }

    @Override

    public void focusGained(java.awt.event.FocusEvent evt) {

        Object o = evt.getSource();

        if(o instanceof javax.swing.JTextField){

            javax.swing.JTextField txt = (javax.swing.JTextField) o;

            txt.setSelectionStart(0);

            txt.setSelectionEnd(txt.getText().length());

        }

    }

}

JTextBox cajaDeTexto = new JTextBox("Valor por defecto");

cajaDeTexto.addFocusListener( new FullSelectorListener() );