5. Design Patterns: Elements of Reusable Object-Oriented Software
Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides


Design Patterns is a modern classic in the literature of object-oriented development, offering timeless and elegant solutions to common problems in software design. It describes patterns for managing object creation, composing objects into larger structures, and coordinating control flow between objects. The book provides numerous examples where using composition rather than inheritance can improve the reusability and flexibility of code. Note, though, that it’s not a tutorial but a catalog that you can use to find an object-oriented design pattern that’s appropriate for the needs of your particular application–a selection for virtuoso programmers who appreciate (or require) consistent, well-engineered object-oriented designs.

4. Refactoring: Improving the Design of Existing Code
Martin Fowler


For more than twenty years, experienced programmers worldwide have relied on Martin Fowler’s Refactoring to improve the design of existing code and to enhance software maintainability, as well as to make existing code easier to understand.

Explains what refactoring is; why you should refactor; how to recognize code that needs refactoring; and how to actually do it successfully, no matter what language you use.

You can understand the process and general principles of refactoring. You can quickly apply useful refactorings to make a program easier to comprehend and change. You will be able to recognize “bad smells” in code that signal opportunities to refactor. Moreover, it helps you explore the refactorings, each with explanations, motivation, mechanics, and simple examples. It also shows you how to build solid tests for your refactorings. And last very important point is it also helps you to recognize tradeoffs and obstacles to refactoring.