Question:How do we define constant variables in OOP and how do we create constant variable with define() function? Show with an example. 

Question:
What is extends, implements, interface, abstract, class, new, static, and instanceof keywords used for?
 

Question:
What are __toString(), __autoload(), __construct(), __destruct(),__set(),__get(),__clone() functions? Briefly explain.
 

Question:How do we invoke member functions and property in OOP? 

Question:How do we invoke parent Constructors?