Mithat Konar (the wiki)

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~~SLIDESHOW~~
====== Object-Orientation Fundamentals ======
Mithat Konar
===== Why object-orientation? =====
  * **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.

===== Procedural thinking =====
  * Break down large problems into functions or procedures.
  * //What needs to happen?//
  * "Verb" oriented.

===== Object-oriented thinking =====
  * Break down large problems into the components (objects) that make up the problem.
  * How do they behave?
  * How do they interact?
  * "Noun" oriented.

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

===== Object-oriented concepts =====

  * 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.

===== State =====

  * 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.

===== Behavior =====

  * 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).

===== Encapsulation =====

  * 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**.

===== Protection =====

  * 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.

===== Objects =====

  * 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.

===== Class-based object-orientation =====

  * My Farberware 4241 microwave.\\ 
{{:python:about_python:farberware4241-200.jpeg?nolink|}}
  * 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.

===== Class-based object-orientation =====

  * 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 =====

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