Software Architect's Handbook

How to avoid duplication

DRYness can be achieved by being mindful and taking action when appropriate. If you find yourself copying and pasting code, or simply writing code that is identical or similar to existing code, think about what you are trying to accomplish and how it can be made reusable.

Duplication in logic can be eliminated by abstraction. This concept is referred to as the abstraction principle (or the principle of abstraction). The principle is consistent with the DRY principle and is a way to reduce duplication. The code that is needed in multiple places should be abstracted out, and the locations that need it can then be routed through the abstraction. Some refactoring may be necessary to make it generic enough to be reused, ...