Open Closed Principle (OCP) states that,
Software entities (Classes, modules, functions) should be OPEN for EXTENSION, CLOSED for MODIFICATION.
Lets try to reflect on the above statement- software entities once written shouldn’t be modified to add new functionality, instead one has to extend the same to add new functionality. In otherwords you don’t touch the existing modules thereby not disturbing the existing functionality, instead you extend the modules to implement the new requirement. So your code is less rigid and fragile and also extensible.
OCP term was coined by Bertnard Meyer.
How can we confirm to OCP principle?
Its simple- Allow the modules (classes) to depend on the abstractions, there by new features can be added by creating new extensions of these abstractions.