/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
import java.awt.KeyboardFocusManager;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.Random;
 
import javax.swing.BoxLayout;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	private final static int FILAS = 50; 
	private final static String nombresDeColumna[] = 
	        { "Nombre" };
	private final static String[] datos = { "Jordi" , "Castilla",  "Mymike",  "Mine",  "Luiggi", "Mendoza", "Super", "Falete" };
	private final static Random rnd = new Random();
 
	public static void main (String[] args) throws java.lang.Exception
	{
		final JPanel contenedor = new JPanel();
		contenedor.setLayout(new BoxLayout(contenedor, BoxLayout.Y_AXIS));
		contenedor.add(new JLabel("Usa tabulador para cambiar de fila."));
		JTextField campo = null;
		for (int i = 0; i < FILAS; i++) {
			campo = new JTextField("" + i);
			campo.setText(datos[rnd.nextInt(datos.length)]);
			campo.setName("campo #" + i);
			contenedor.add(campo);
		}
 
		KeyboardFocusManager.getCurrentKeyboardFocusManager().addPropertyChangeListener("focusOwner", new PropertyChangeListener() {
			public void propertyChange(PropertyChangeEvent evt) {
				// ignoramos todo lo que no sea un componente
				if (!(evt.getNewValue() instanceof JComponent)) {
					return;
				}
				// cojemos el elemento, miramos que este en el contenedor 
				JComponent elementoEnfocado = (JComponent) evt.getNewValue();
				if (contenedor.isAncestorOf(elementoEnfocado)) {
					// y si es candidato, "enfocamos" el contenedor a la altura del elemento
					contenedor.scrollRectToVisible(elementoEnfocado.getBounds());
					System.out.println("Vamos al "+ elementoEnfocado.getName());
				}
			}
		});
 
		JFrame window = new JFrame("Siguiendo el foco");
		window.setContentPane(new JScrollPane(contenedor));
		window.setSize(400, 600);
		window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		window.setVisible(true);
 
		// seleccionamos el ultimo campo para ver como se comporta al recibir el foco.
		campo.requestFocusInWindow();
 
	}
}

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