How to save multiple classes in 1 file?

[Patryk Ka]

I'm beginner in Java code, and I can't find any way to add new classes to existing file with saved before classes.

I have to write little RentCar database (without MySQL etc.). When I use my "Add new car to the list" code it clean up previous position and make file empty before save. How set the file pointer at the end of file to add new positions?

[Sean Pedersen]

There can only be one public class per file, the rest must be private.