[sottovento]

Scusa, la MouseListener. Non hai bisogno della MouseMotionListener.

Ti ho scritto un esempio. ATTENZIONE - e' in Java 8

package com.sottovento;

import java.awt.BorderLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class TestMouse extends JFrame
{
    public TestMouse()
    {
        buildGUI();
    }

    private void buildGUI()
    {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        JLabel lbl;
        JPanel southPanel = new JPanel();
        final JTextField tf = new JTextField(30);
        tf.setEditable(false);
        southPanel.add(tf);
        getContentPane().add(southPanel, BorderLayout.SOUTH);

        JPanel northPanel = new JPanel();
        northPanel.add(lbl = new JLabel("GIULIO"));
        lbl.addMouseListener(new MouseAdapter() {
                @Override
                public void mouseEntered(MouseEvent evt) {
                    tf.setText("GIULIO");
                }
            });
        northPanel.add(lbl = new JLabel("LUCA"));
        lbl.addMouseListener(new MouseAdapter() {
                @Override
                public void mouseEntered(MouseEvent evt) {
                    tf.setText("LUCA");
                }
            });
        northPanel.add(lbl = new JLabel("FRANCESCO"));
        lbl.addMouseListener(new MouseAdapter() {
                @Override
                public void mouseEntered(MouseEvent evt) {
                    tf.setText("FRANCESCO");
                }
            });
        getContentPane().add(northPanel, BorderLayout.NORTH);

        setLocationRelativeTo(null);
        pack();
    }

    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(() -> new TestMouse().setVisible(true));
    }
}