Variables are usually stored in RAM. This is either on the Heap (e.g. global variables, static variables in methods/functions) or on the Stack (e.g. non-static variables declared within a method/function). Stack and Heap are both RAM, just different locations.

Are variables stored in main memory?

This memory is used for storing the frequently executed code (binary data), program variables, etc. The below memory segments talks about the same: Typically there are three types of variables: Local variables (also called as automatic variables in C)

Where the variables are stored in Java?

All objects in Java are stored on the heap. The "variables" that hold references to them can be on the stack or they can be contained in other objects (then they are not really variables, but fields), which puts them on the heap also. The Class objects that define Classes are also heap objects.