Open Closed Design Principle

In Design principle, SOLID – the "O" in "SOLID" stands for the open/closed principle.

Open Closed principle is a design principle which says that a class, modules and functions should be open for extension but closed for modification.

This principle states that the design and writing of the code should be done in a way that new functionality should be added with minimum changes in the existing code (tested code). The design should be done in a way to allow the adding of new functionality as new classes, keeping as much as possible existing code unchanged.

Benefit of Open Closed Design Principle:

1) Application will be more robust because we are not changing already tested class.

2) Flexible because we can easily accommodate new requirements.

3) Easy to test and less error prone.