💁  In C#, all types, predefined and user-defined, reference types and value types, inherit directly or indirectly from Object. So basically it is the base class for all the data types in C#. Before assigning values, it needs type conversion. When a variable of a value type is converted to an object, it’s called boxing. When a variable of type object is converted to a value type, it’s called unboxing.

• Reference Data Types: will contain a memory address of variable value because the reference types won’t store the variable value directly in memory. The built-in reference types are string, and object.
• Primitive data type: int, float, double, …

💥 More simply, when declaring the basic data types, the value is stored on the Stack and Boxing memory is the transfer from the Stack to the Heap.

Boxing In C#

• Value Type variables are always stored in Stack memory, while Reference Type variables are stored in Heap memory.

Example Boxing:

int num = 123; // 123 will be assigned to num (Stack)
Object Obj = num; // Boxing (Move Stack to Heap)

• Description
  • First, we declare a Value Type variable num of the type int with value 123 (Stack).
  • We create a Reference Type variable obj of the type Object and assign num to it. 123 will be copied and stored in the Reference Type variable obj (HEAP).

Unboxing In C#

• Casting an object to a value type is called unboxing.
• Heap will be copied to Stack.
• Unboxing of a null object or casting the object as an incompatible data type, the program throws exceptions.

Example Unboxing:

int num = 23;         // value type is int and assigned value 23
Object Obj = num;    // Boxing
int i = (int)Obj;    // Unboxing - casting

Boxing and Unboxing in Java