Are there any rules for OOP?

Question

Recently I heard that there are 9 rules for OOP(Java). I know only four as Abstraction, Polymorphism, Inheritance and Encapsulation. Are there any more rules for OOP?

Answer 1

These OO principles are straight from Head First Design Patterns:

• Encapsulate what Varies
• Program to an Interface, rather than an Implementation
• Favour Composition over Inheritance
• A Class should have only one reason to Change (Single Responsibility Principle)
• Sub-Types must be substitutable for their Base (Liskov Substitition Principle)
• Classes shoule be Open for extension, but Closed for Modification (Open-Closed Principle)