I have got my certification of completion of Java Programming Diploma last week.
The most usefull thing i got from this course is the stong concept of OOP in java which helped me a lot in PHP especially after working with PHP5 which is diversed to the OOP conecpt. and also using Zend Framework.
i would like to thank the one who encouraged me to take it. ; i am satisfied with it and it was something i must have taken.
i have written some Java tutorials here, i will right more when i am done with the couple of projects i am taking care of now.