This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Beginners to Java could do much worse than going through the Java tutorial. If you click on "big index" on the right you can navigate to whichever page you want, including the page about comboboxes.
You will find that the Java tutorial uses the construct "addActionListener(this)" which I have just described as an abomination, on this thread. If you follow the links I have posted you get other threads where the same thing is discussed and some of us have posted our opinions.