JavaCard OS

Hi!
I have a java card with an applet installed. The things that I only know is the applet -AID and there is data stored in simple byte arrays format in the applet, but I don't know APDUs that applet supports.

Here are my questions:
- Is there any other storage methods the applet is using for data storage?
- For the scenario I mentioned, how can I read data from applet?

Thanks a lot for your time and reply !

- Is there any other storage methods the applet is using for data storage?

A: It can also store data in ISO7816 file format.

- For the scenario I mentioned, how can I read data from applet?

A: If you know nothing about the APDUs of the applet, you can not read data from the applet.