Compile and run the following codes, you can find that under jdk1.2 ComboBoxModel.setSelectedItem() creates ItemEvent, but under jdk1.4, no ItemEvent is created.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Test {
    public Test() {
        JFrame f = new JFrame("Test ComboBox");
JComboBox combo = new JComboBox();
combo.setModel(new MyModel());
combo.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent evt) {
System.out.println("selection changed: " + evt.getItem());
}
});

f.getContentPane().setLayout(new FlowLayout());
f.getContentPane().add(combo);
((MyModel)combo.getModel()).setSelectedItem("bac");
f.setSize(200, 200);
f.setVisible(true);
    }
    
    public static void main(String[] args) {
        new Test();
    }
}

class MyModel extends AbstractListModel implements ComboBoxModel {
    String[] items = {"abc", "bac", "cba"};
    Object currentValue;

    public void setSelectedItem(Object anObject) {
        currentValue = anObject;
        fireContentsChanged(this, -1, -1);
    }

    public Object getSelectedItem() {
        return currentValue;
    }

    public Object getElementAt(int index) {
        return items[index];
    }

    public int getSize() {
        return items.length;
    }
}