Inheritance is a central idea that distinguishes object-oriented methods from other methods.

Encapsulation: The unit of encapsulation in an object-oriented system is the object and information can only be exchanged between objects through interfaces. Messages: Messages are the means of communication between objects where one object requests a service by sending a message to another object. Polymorphism: Polymorphism means that the same operation can be interpreted differently when applied to different objects and produce different execution results