#34 – The object Type

In the .NET Framework, all types are derived from System.Object.  In C#, the object keyword is a synonym for this same type.  System.Object is the base class for all other types in .NET, including built-in types and custom types.

In C#, all types can be upcast to object.

 string msg = "A string";
 int n = 42;
 Person me = new Person("Sean", 46);

 // Can assign anything to an object variable
 object o = msg;
 o = n;
 o = me;

Any class that you create in C# is automatically derived from object.

The object type defines the following instance methods:

  • bool Equals(object)
  • void Finalize()
  • int GetHashCode()
  • Type GetType()
  • object MemberwiseClone()
  • string ToString()

The object type defines the following static methods:

  • bool Equals(object, object)
  • bool ReferenceEquals(object, object)

This means that every new class automatically inherits these methods.

 Person me = new Person("Sean", 46);
 int hash = me.GetHashCode();