JComboBox with custom label

Example.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.ListDataListener;
import javax.swing.plaf.basic.BasicComboBoxEditor;

public class Example extends JPanel {
    static class ActiveComboItem {
        private final Object item;

        public ActiveComboItem(Object item) { this.item = item; }

        @Override
        public boolean equals(Object other) {
            return item == null ? other == null : item.equals(other);
        }

        @Override
        public String toString() { return String.format("Animal: %s", item); }
    }

    public Example() {
        super(new BorderLayout());

        final String[] animals = { "Cow", "Dolphin", "Pig", "Rat" };

        JComboBox animalCombo = new JComboBox(animals);

        animalCombo.setModel(new DefaultComboBoxModel(animals) {
            private Object selected;

            public void setSelectedItem(Object anItem) {
                selected = anItem;
            }

            public Object getSelectedItem() {
                return new ActiveComboItem(selected);
            }
        });

        add(animalCombo, BorderLayout.PAGE_START);
        setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JComponent newContentPane = new Example();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() { createAndShowGUI(); }
        });
    }
}