Abstraction, Encapsulation & Information Hiding

Abstraction

Abstraction: reasoning about the essential properties of an object, ignoring unimportant details.

• Extracts the essential details about an item, or a group of items, while ignoring the inessential details.
• In software development manages complexity by providing an interface to a module.

Steps

• Examine a complex problem.
• Distinguish between high- and low-level information.
• Extract high level information.
• Solve less complex problem.

Examples

• Apple Corer
  • No abstraction; must understand process to make it work.
• Microwave
  • Completely abstract interface.
  • Input: food to be headed and setting.
  • Output: hot food.
• Barbecue
  • Would be convenient to have an abstract interface.
  • In reality the cook must understand the process in detail.
• Sink/ Tap
  • Completely abstract.
  • Input: turn tap.
  • Output: water.

Order by increasing level of abstraction:

1. Apple corer.
2. BBQ.
3. Sink/ Tap.
4. Microwave.

Encapsulation

Encapsulation refers to building a capsule, in the case a conceptual barrier, around some collection of things.

• Enclosing one or more items within a (physical or logical) container.
• Although often used as a method of disallowing access to or knowledge of internal structures of an implementation, does not in itself imply any sort of information hiding or protection.

Information Hiding

• The process of hiding the implementation details of an object.
• It is a result of encapsulation or abstraction/ how they are achieved.

Summary

• Abstraction, information hiding, and encapsulation are very different, but highly-related, concepts.
• One could argue that abstraction is a technique that help us identify which specific information should be visible, and which information should be hidden.
• Encapsulation is then the technique for packaging the information in such a way as to hide what should be hidden, and make visible what is intended to be visible.
• If encapsulation was the same thing as information hiding, then one might make the argument that everything that was encapsulated was also hidden– This is not obviously not true.