Introduction to Object Oriented Programming

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Introduction to Object Oriented Programming

• Java

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Resources

• If you are new to programming in Java, there is
  an online book which is serves as a good
  introduction
• ?Thinking in Java 3rd edition
• This can be found at
• http//www.mindview.net/Books/TIJ/

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Development Environment

• You can use the command line and notepad to edit
  and compile java programs.
• You can also use jedit
• BlueJ is a tool which will help you format code,
  compile and test your programs.

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OOP Introduction

• Introduced in the 60s as a proposed
• solution to the sprawl of software
• Allowed designers to describe the system entities
  in plain language and design functions and
  attributes for each entity.
• The interaction or interfaces between the
  entities can also be designed easily.

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An OO Approach

• class Student
• / attributes /
• String name
• int age
• int courseNumber
• int fees
• boolean enrolled
• / Methods /
• public getName() ...
• public int getAge() ...
• public int getFees() ...

class StudentRecords / attributes / Student
database Course allCourses / Methods
/ public void enrollStudent(Student s) ...
public void disenrollStudent (Student s) ...
public int getTotalStudents() ...
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Advantages of OO Programming

• The software is modular and reusable
• i.e. we could reuse our code for Student in an
  examRecords system
• It is extendable, and maintainable
• i.e. if we decided to store students mobile phone
  numbers, it'd just be a small change to the
  Student class.

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OO Programming Vocabulary

• ? class
• ? object
• ? method/attribute
• ? inheritance
• ? encapsulation
• ? abstraction
• ? polymorphism

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Class

• A class is a definition of a well defined entity,
  containing attributes and methods. This is a
  real world entity
• class Employees

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Object

• An object is an instance of a class.
• e.g. Employee e1 new Employee()
• e1 is now an object of type Employee.

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Method

• A method is simply a well defined function within
  a class.
• Example methods in Employee...
• getSalary()
• getDOB()
• add()
• remove()

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Attribute

• ? An attribute is an instance variable
• which represents some data within a class. For
  example, all employees have a name and a salary.
• so...
• ? class Student
• String name
• float salary
• ..etc.

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Inheritance

• ? Inheritance allows you to define classes
• which inherit the behaviour and attributes of
• other classes.
• ? For example, you may have one Employee
• class, but 3 different types of employees
• (permanent staff, part time staff and managers).
• Rather than write 3 entirely separate classes
• you can inherit the standard employee
• characteristics from a base class.

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Inheritance Example
Employee

• Permanent

PartTime
Manager
forthnightSalary weeklySalary
monthlySalary
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Advantages of this approach

• Less code, therefore easier to maintain
• Reusable Employee class

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Encapsulation

• ? We've seen how to specify the
• behaviour of an object, the idea of
• encapsulation is to hide the details of
• how something is achieved.
• ? e.g. If you are using a class that
• someone else has written, you want to
• be able to call a method (Save File for
• example) without knowing what is
• going on in the background.

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Abstraction

• ? Abstraction a principle used to enable
• inheritance.
• ? Using abstraction you develop general
• classes that are appropriate to the
• problem, and then for specific problems
• inherit from these general classes.
• ? e.g. an Employee class models the typical
• behaviours of employees, but for parttime staff
• you'll need more specific methods.

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Polymorphism

• ? Polymorphism is a type of encapsulation that is
  aimed at decoupling software systems.
• ? Polymorphism literally means many
• forms, and its idea is to allow subclasses to
  have their own specific implementations of
  methods.
• e.g. calculateSalary is a different process
• for our three types of employee.