Where is a resource or object reference usually stored in the system?

In Java, a reference to a resource or object is usually stored in a variable, which is kept on the stack (if it is a local variable) or in a field of an object (if it is a class field). The actual object or resource is located in the heap, and the variable contains a reference to it. For example:

String str = new String("Example");

Here, str is a reference that points to an object in the heap.

References can also be stored in collections, arrays, or other data structures, but in any case, they are pointers to objects in memory, not the objects themselves.