Hi,
The OnTick method is indeed called by tick prices and your assumption is correct.
As you posted under Visual Jforex forum, I've made a quick example in vfs format. I've added a print function to the java code as well.
You can import the vjs file from Visual JForex
https://www.dukascopy.com/vjforex/ File > import
I suggest to test using an instrument that is not quoting frequently such as some indices or stocks.
If you need help for your code, please post your questions under automated trading section
Cheers