OO provides a simple uniform framework basic types are classes also and can partake in all OO games. Good implementation avoids negative consequences from the decision to make all types classes. Uniform access preserves autonomy of components by hiding implementation. Every operation of OO computation is relative to a certain object, the current instance at the time of the operation's execution. No software ever gets executed except as part of a routine call.
Every call has a target.
Hiding Full disclosure Restricting client Access How to build executable systems from individual classes. A system is closed iff its class set contains all classes needed by the root class. The top, or fundamental component of the system's architecture. Assembling a System.