Transcript Introduction to Object Oriented Programming

Introduction to Object
Oriented
Programming
Java
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/
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.
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.
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()
{ ... }
}
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.
OO Programming Vocabulary
● class
● object
● method/attribute
● inheritance
● encapsulation
● abstraction
● polymorphism
Class
A class is a definition of a well defined
entity, containing attributes and methods.
This is a real world entity
class Employees {
}
Object
 An object is an instance of a class.
 e.g. Employee e1 = new Employee();
 e1 is now an object of type Employee.
Method
 A method is simply a well defined
function within a class.
 Example methods in Employee...
 getSalary();
 getDOB();
 add();
 remove();
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.
}
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.
Inheritance Example
Employee
Permanent
forthnightSalary
PartTime
Manager
weeklySalary
monthlySalary
Advantages of this approach
 Less code, therefore easier to maintain
 Reusable Employee class
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.
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.
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.