You can always check your mobile phone user manual to know what platform your phone is running on. However if you find hard to find it out then you can always use the internet.
To start off, visit GSM Arena at www.gsmarena.com.
If you know the brand and model number of your phone, then simply search for the same in the search box provided at the top right corner. Alternatively if you are unsure about the model number of your phone, just use the listing of brands on the left to browse through the different models in a pictorial grid – after all you know what your mobile phone looks like!.
Once you locate your phone through either method, click on it to open its specification sheet. For phones where the OS is not listed, or for those operating systems that are not listed, you will need to know whether your phone supports Java. It is a rare that smart phones don’t have java support.
Of course if that doesn’t help then you can always use the Google or search for Wikipedia entry. You can also call your customer service for your brand and ask them to help you out with this information.