A DESCRIPTION OF THE REQUEST :
JComboBox.getSelectedIndex() traverses the data list looking for the first match:
    public int getSelectedIndex() {
        Object sObject = dataModel.getSelectedItem();
        int i,c;
        Object obj;

        for ( i=0,c=dataModel.getSize();i<c;i++ ) {
            obj = dataModel.getElementAt(i);
            if ( obj != null && obj.equals(sObject) )
                return i;
        }
        return -1;
    }



  Given that the selected item's index is known when set, couldn't the JComboBox cache this index and return that value each time instead of iterating/looking. If the underlying model changes the JComboBox could do a rescan then and recache the selected index.

JUSTIFICATION :
will be quicker

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
quick retrieval of the index
ACTUAL -
a possible complete iteration of the model

---------- BEGIN SOURCE ----------
import javax.swing.*;
import java.awt.*;


public class JComboBoxSelectedIndex implements Runnable{

    public void run(){
Integer[] data = new Integer[Integer.MAX_VALUE/100];
        for(int i = 0; i < Integer.MAX_VALUE/100; i++)
            data[i] = i;
        JComboBox jcb = new JComboBox(data);
        jcb.setSelectedIndex(Integer.MAX_VALUE/100 -1);
        System.out.println("GETTING SELECTED INDEX....");
        long time1 = System.currentTimeMillis();
        jcb.getSelectedIndex();
        long time2 = System.currentTimeMillis();
        System.out.println("Took:: " + (time2 -time1));


    }

    public static void main(String ... args){
        SwingUtilities.invokeLater(new JComboBoxSelectedIndex());
    }

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
The user could override the set methods and cache there.