ObjectOriented Programming Concepts

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Object-Oriented Programming Concepts
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• What are Objects?
• What are Classes?
• What are Messages?
• What is Inheritance?

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What Are Objects?

• Software objects model read-world objects or
  abstract concepts
• dog, bicycle, queue
• Real-world objects have states and behaviors
• Dogs' states name, color, breed, hungry
• Dogs' behaviors barking fetching
• How do Software objects implement real-world
  objects?
• Use variables to implement states
• Use methods to implement behaviors
• An object is a software bundle of variables and
  related methods

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Visual Representation of A Software Object
Variable
Method
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Software Bicycle

• Instance Variables and Instance Method

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Encapsulation

• The objects' variables make up the center of the
  object.
• Methods surround and hide the object's center
  from other objects.
• Benefit of encapsulation
• Modularity
• Information hiding
• For implementation or efficiency reasons, an
  object may wish to expose some of its variables
  or hide some of its methods.

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What Are Classes?

• A class is a blueprint or prototype defining the
  variables and methods common to all objects of a
  certain kind.
• An object is an instance of a certain class.
• After you have created a class, you must create
  an instance of it before you can use.
• Class variables and class methods
• The benefit of Classes Reusability

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Visual Representation of A Software Class
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What Are Messages?

• Software objects interact and communicate with
  each other by sending messages to each other.

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More on Messages

• Components of a Message
• The object to whom the message is addressed (Your
  Bicycle)
• The name of the method to perform(changeGears)
• Any parameters needed by the method (low gear)
• The Benefits of Messages
• Messages passing supports all possible
  interactions between objects (aside from direct
  variable access)
• Objects dont need to be in the same process or
  even on the same machine to send and receive
  messages.

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What is Inheritance?

• Inheritance allows classes to be defined in terms
  of other classes
• superclass and subclass
• Each subclass inherits variables and methods from
  its superclass.
• Subclasses can add variables and methods to the
  ones they inherit from the superclass.
• Subclasses can also override inherited method and
  provide specialized implementations for those
  methods.
• Inheritance or class hierarchy

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Benefits of Inheritance

• Programmers can reuse the code in the superclass
  many times.
• Programmers can implement superclasses called
  abstract classes
• Abstract class defines generic behaviors
• Define and may partially implement the behavior
  but much of the class is undefined and
  unimplemented. Other programmers fill in the
  details with specialized subclasses.

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Message Example
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Inheritance Example