Which is pillars of oops?

Basically oops pillars is 

1.Abstraction 

2. Encapsulation

3. Inheritance

4 .Polymorphism 

In Polymorphism we divided into 2 categories 

1 Overloading

   a.Operator overloading

   b.Method overloading

2. Overriding

   a. Compiletime Polymorphism

   b. Runtime polymorphsim