what is the difference between refernce an instance of a class.can u provide me some clear exemples.

Reference variables holds memory location where the object has been created. When we destroy an object, actually we destroy the reference so as the object iteself.

Customer cust = new Customer();
Here, cust is an object reference variable (which points to the memory location where the Customer instance is created). So, a Customer instance is created and the reference is stored in the reference variable.