Object-Orientation Fundamentals

Mithat Konar

• Object-oriented programming came about to support object-oriented analysis and design (OOAD).
• OOAD created to solve issues involved in designing and managing large applications.

• Break down large problems into functions or procedures.
• What needs to happen?
• “Verb” oriented.

• Break down large problems into the components (objects) that make up the problem.
• How do they behave?
• How do they interact?
• “Noun” oriented.

• Possible to implement OOAD in any language.
• Easier and more robust when language has support for defining and using objects: an object-oriented language.

• The concept of “object” in computing comes directly from the concept of “object” in the real world.
• Critical ideas:
  • state
  • behavior
  • encapsulation and protection
  • self-governance
• Let’s explore this with the example of a microwave oven.

• At any given instant, a microwave oven has a particular state.
  • Is it cooking?
  • At what power level?
  • How much cooking time is left?
  • What time does it think it is?
• These attributes (and others) collectively define the oven’s state.

• A microwave also has predefined behavior:
  • Push the “1” button → start cooking at maximum power for one minute.
  • Push the “+30 sec” button → add 30 seconds to the cooking time if it’s already cooking or start cooking for 30 seconds at maximum power.
  • Push a magical combination of buttons → set the internal clock.
• These operations (and others) collectively define the oven’s behavior.
• interface: the public-facing behavior (i.e., the operations a user can engage).

• User changes the state of the oven only by engaging one or more of the operations in the oven’s interface.
• Don’t need to know how a magnetron, the clock’s electronics, or anything else works to use the oven.
• Only need to know what changes in state to expect from the “cook 1 minute” or “add 30 seconds” operations.
• “I don’t care about how it works—I only need to know what it does,” is part of encapsulation.

• Oven internals are protected against unwanted fiddling by screws and scary labels—for a reason.
  • “No user serviceable parts inside.”
• protection: keeping the user out of stuff that the user should not be allowed to access.

• The microwave oven takes responsibility for managing its own state using a set of predetermined behaviors: it’s self-governing.
• object-oriented language: a language that let you create self-governing entities.
• Self-governing entities are called objects.
• object: a program entity that encapsulates state (via attributes) and behavior (via operations involving those attributes) for some meaningful abstraction.

• My Farberware 4241 microwave.
  

• All Farberware 4241s made from a master plan.
  • Defines what the Farberware 4241 is.
• In computing terminology, the master plan is a class.
• A class contains all the specifications needed to make a particular kind of object.

• Objects that have been created from classes are also called instances.
• The process of creating an instance from a class definition is called instantiation.

• Prototype-based object-orientation: used in JavaScript and some other languages.
• Currently less common than class-based OOP.