package JavaCombo;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 class JavaCombo extends JFrame{
    private JComboBox Box;
    private JLabel picture;
    private static String[] filename = {"Smiley1.jpg","Smiley2.jpg"};
    private Icon[] pics = {new ImageIcon(getClass().getResource(filename[0])),new ImageIcon(getClass().getResource(filename[1]))};
    public JavaCombo(){
        super("Java Combo");
        setLayout(new FlowLayout());
        Box = new JComboBox(filename);
        Box.addItemListener(
            new ItemListener(){
                public void itemStateChanged(ItemEvent event){
                    if(event.getStateChange()==ItemEvent.SELECTED)
                        picture.setIcon(pics[Box.getSelectedIndex()]);
                }
            }
    );
    add(Box);
    picture = new JLabel(pics[0]);
    add(picture);
}
}

===================================================================================================

package JavaCombo;
import javax.swing.JFrame;

public class JavaComboTest {
    public static void main(String[] args){
        JavaCombo myJavaCombo = new JavaCombo();
        myJavaCombo.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        myJavaCombo.setSize(300,120);
        myJavaCombo.setVisible(true);
    }

}