Transcript Lecture 1: An Introduction to Java

Lecture 1: An Introduction to
Java
What is Java?
• Programming language developed by Sun
Microsystems in 1995
– Inherits its syntax from c
– Adapted the object model from C++
• Object Oriented Language
• Compiled and Interpreted
• Both WWW (applet) and stand alone
(Application)
Applications and Applets
• Applications
• Applets
Birth and Growth of Java
• Invented by James Gosling in 1995 – originally not
intended as a new language
• Originally intended for writing programs that control
consumer appliances such as toasters and microwave
ovens.
• Sun commissioned by Time-Warner to develop language
• Time Warner lost patience with delays
– Sun lost contract
– Sun gained new language
• Fundamental concept: Write once – Run Anywhere
(write on one O/S run on any)
Object Orientation
• Object Oriented (oo) philosophy operates
by modeling real world entities within a
computer program. This involves using
different characteristics for objects.
Objects then interact by passing
messages
• Object oriented design
– A software design method that models the
characteristics of abstract or real objects
using classes and objects
Objects and Classes
Object
• An object is a combination of some data
(variables) and some actions (methods)
• Objects are the principal building blocks of
object oriented programs. Each object is a
programming unit consisting of data (instance
variables) and functionality (instance methods)
Class
• A template or type describing the fields and
methods that we group together to represent
something
Objects and Classes
• A class is a generalisation of an object – it is the
blueprint from which instances of objects can be created.
Once a class is designed, many objects can be
constructed with the same behaviour
• Example: Student
• Students have certain characterisitics that distinguish
them from each other……
• Name
• University
• Course
• Age
• Gender
Objects and Classes
• An object is something you can use
• A class is a description of how to create an
object
• Objects are ‘real’ classes are not.
•
Class (Template)
Name
University
Course
Age
Gender
Marie
Trinity
History
21
Female
Frank
Ucc
BIS
20
Male
Student Example
• Marie and Frank are two instances of a
student
• They have the same general information
but can be differentiated by the specific
values assigned to them
• We can pass messages to each student
object to find out their characteristics:
• What is your name?
(frank)
• What is your course?
(BIS)