What is the base class for all data types in C#.NET?

Object is the base class for all data types in C#. The Object Type is the ultimate base class for all data types in C# Common Type System (CTS). The object is an alias for System.Object class.

When a value type is converted to object type, it is called boxing and on the other hand, when an object type is converted to a value type, it is called unboxing.

Syntax

Following is the syntax for declaring an object variable −

object variableName;
object variableName = value;

Following is the syntax for boxing and unboxing −

// Boxing: value type to object
object obj = 10;

// Unboxing: object to value type
int num = (int)obj;

Understanding the Object Class Hierarchy

Every type in C# ultimately derives from System.Object, whether directly or indirectly. This includes both value types and reference types.

Using Object Data Type

Example

using System;

namespace Demo {
   class ObjectClass {
      public int x = 56;
   }

   class MyApplication {
      static void Main() {
         object obj;
         obj = 96;
         Console.WriteLine(obj);
         obj = new ObjectClass();
         ObjectClass newRef;
         newRef = (ObjectClass)obj;
         Console.WriteLine(newRef.x);
      }
   }
}

The output of the above code is −

96
56

Boxing and Unboxing Example

Example

using System;

class Program {
   static void Main() {
      // Boxing: Converting value type to object
      int num = 25;
      object obj = num;
      Console.WriteLine("Boxed value: " + obj);
      Console.WriteLine("Type: " + obj.GetType());

      // Unboxing: Converting object back to value type
      int unboxedNum = (int)obj;
      Console.WriteLine("Unboxed value: " + unboxedNum);

      // Boxing with different data types
      object boolObj = true;
      object charObj = 'A';
      object stringObj = "Hello";

      Console.WriteLine("Bool: " + boolObj);
      Console.WriteLine("Char: " + charObj);
      Console.WriteLine("String: " + stringObj);
   }
}

The output of the above code is −

Boxed value: 25
Type: System.Int32
Unboxed value: 25
Bool: True
Char: A
String: Hello

Common Object Methods

Since all types inherit from System.Object, they all inherit these common methods −

Example

using System;

class Student {
   public string Name { get; set; }
   public int Age { get; set; }

   public Student(string name, int age) {
      Name = name;
      Age = age;
   }

   public override string ToString() {
      return $"Student: {Name}, Age: {Age}";
   }
}

class Program {
   static void Main() {
      Student student = new Student("John", 20);
      
      // Using inherited Object methods
      Console.WriteLine("ToString(): " + student.ToString());
      Console.WriteLine("GetType(): " + student.GetType());
      Console.WriteLine("GetHashCode(): " + student.GetHashCode());
      
      // Comparing references
      Student student2 = student;
      Console.WriteLine("ReferenceEquals: " + ReferenceEquals(student, student2));
   }
}

The output of the above code is −

ToString(): Student: John, Age: 20
GetType(): Student
GetHashCode(): 58225482
ReferenceEquals: True

Conclusion

System.Object is the ultimate base class for all data types in C#, providing common functionality like ToString(), GetType(), and Equals(). Understanding boxing and unboxing is essential when working with value types as objects, as it affects performance and behavior in your applications.