Deisgn Patterns Principles

Design Patterns Principles

Design Principles List

• Identify the aspects of your application that vary and separate them from what stays the same.
• Program to an interface, not an implementation
• Favor composition over inheritance. (Has-a instead of Is-a)
• Strive for loosely coupled design between objects that interact. (minimal interdependency on other objects)
• Classes should be open for extension, but closed for modification. that is, such an entity can allow its behavior to be extended without modifying its source code.
• Depend upon abstractions. Do not depend on concrete classes.
•  Principle of least knowledge - talk only to your immediate friends.

 Bullet Points

• Knowing the OO basics does not make you a good OO designer 
• Good OO designs are reusable, Extensible and maintainable.
• Patterns re proven object orientated experience.
• Patterns don't give you code, they give you general solutions to design problems.
• Patterns aren't invented, they are discovered 
• Most patterns principles address issues of change in software
• Most patterns allow some part of a system to vary interdependently of all other parts.
• We often try to take what varies and encapsulate it
• Patterns provide a shared language that can maximize the value of your communication with other developers.