Write a Java program which adds all numbers that are multiples of either 7 or 9 up to 600. Ensure that numbers like 63 are added only once in the sum.

Thanks for help

You just copy/pasted your assignment without even a moment taken to explain what help you need. That's highly disrepestectful to the many people who give their time to help others here.

There are lots of people here who will freely give their time to help you become the best Java programmer you can be. There's nobody here who is interested in helping you cheat or doing your homework for you.

DaniWeb Member Rules (which you agreed to when you signed up) include:
"Do provide evidence of having done some work yourself if posting questions from school or work assignments"
http://www.daniweb.com/community/rules

Post what you have done so far and someone will help you from there.

I gotta admit,
I have asked random ppl in forums to "help" me with my assignments, but I can assure you that is not the right way to go! I can advise you to grab a priece of paper and write down exactly what your program should do. Then try and do the same thing in phseudo code (not actual code but something resembling it). Finally write your program. I know it is a long process but that is one good way forward which doesn't include breaking forum rules ...
best of luck