The Professionals Point

If we set access specifier of a constructor to private, then that constructor can only be accessed inside the class. A private constructor is mainly used when you want to prevent the class instance from being created outside the class.
This is mainly in the case of singleton class. Singleton classes are employed extensively in concepts like Networking and Database Connectivity. Using private constructor we can ensure that no more than one object can be created at a time....

The diamond problem occurs when two super classes of a class have a common base class.
Suppose there are four classes A, B, C and D. Class B and C inherit class A. Now class B and C contains one copy of all the functions and data members of class A. Class D is derived from class B and C. Now class D contains two copies of all the functions...

In Delphi, we do have static variables, properties, functions and procedures, but instead of the word "static" we refer the word "class". In this tutorial, I have shown the syntax of declaring the static variables, properties, functions and procedures...

In VCL (Visual Component Library) hierarchy, you will find TObject at the top, then TPersistent, then TComponent and then TControl.
TObject >> TPersistent >> TComponent >>TControl
VCL Hierarchy in Delphi