Object oriented software development is something that takes people time to get. Often I find myself pointing people to this this article to sum up why I am doing or something, why something feels right or wrong to me.

This is not a new article – I just find myself pointing people to this better explaination than I could give on more and more occasions.

Summary of principals:

The Open Closed Principle (OCP) ?
A module should be open for extension but closed for modification.

The Liskov Substitution Principle (LSP) ?
Subclasses should be substitutable for their base classes.

The Dependency Inversion Principle (DIP) ?
Depend upon Abstractions. Do not depend upon concretions.

The Interface Segregation Principle (ISP) ?
Many client specific interfaces are better than one general purpose interface

The Release Reuse Equivalency Principle (REP) ?
The granule of reuse is the granule of release.

The Common Closure Principle (CCP) ?
Classes that change together, belong together.

The Common Reuse Principle (CRP) ?
Classes that aren’t reused together should not be grouped together.

The Acyclic Dependencies Principle (ADP) ?
The dependencies betwen packages must not form cycles.

The Stable Dependencies Principle (SDP) ?
Depend in the direction of stability.

The Stable Abstractions Principle (SAP) ?
Stable packages should be abstract packages.

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