Transcript Introduction to Database Development

M1G413283
Introduction to
Programming 2
1. Designing a program
Teaching staff
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Jim Paterson
Room M628
[email protected]
Katrin Hartmann
Room 611
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Online resources
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Blackboard
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Announcements
Assessment information
Course website
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Can be accessed through Blackboard
www.paterson.co.uk/gcal/intro2prog2.shtml
Lecture notes, lab & tutorial sheets, etc
Links to other resources
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Reading
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No set text – notes will be provided
The following books are recommended as
additional reading:
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Objects First with Java: A Practical Introduction
Using BlueJ by David J. Barnes and Michael
Kolling (ISBN 0137005628)
Studying Programming by Sally Fincher (ISBN
1403946876)
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Assessment
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Class test
Lab exercises
PeerWise
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Models in software development
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A software system can be modelled using, for
example, class diagrams
A model of the data in the system can be
used to help design a database
A model can also be used to help design and
create the software application, or program,
which actually carries out the functions of the
system
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Java programs
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A Java program can be:
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A few lines of code which perform a single
function, for example to add two numbers
A large enterprise system consisting of many
Java classes which provide very complex services
Anything in between...
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Java programs
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User interface can be:
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Windows application
Web pages
Web page applets
Phone applications
Games
Embedded
Command line
etc...
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Object-oriented programs
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Java is an object-oriented programming
language
When an object-oriented program is running,
it creates objects which work together, or
collaborate, to perform the required actions
These objects often represent entities in the
system
GCU Tours system has objects representing
customers, bookings, and so on
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Classes and objects
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An OO program creates objects as it runs
Nees to have a template which specifies
what type of object will be created and what
that type of object can do
This template is called a class
In fact, when you write a program, you are
actually writing the templates
An object is a single instance of a class –
there can be many objects of the same type
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Class contents
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A class specifies the following for the objects
it is used to create:
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The name of the type of object (e.g. Customer)
The properties which each object will have (e.g.
name)
The actions which each object can perform (e.g.
change password)
The way in which each object is linked with
other objects (e.g. with Booking objects)
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Other languages
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Other popular object-oriented languages
include C#, Visual Basic.NET, C++, Python
In your university career you will come across
a number of languages
Many of the techniques which you learn with
Java have equivalents in other languages
Once you learn Java it is relatively easy to
adapt to others.
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What do classes represent?
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Information
May be information which needs to be stored
permanently - database
User
-name
-address
-username
-password
-datejoined
Booking
1..1
0..*
-adults
-children
-bookingdate
-status
0..*
1..1
Package
-location
-name
-description
-adultprice
-childprice
-departure
Tour
-departuredate
-offer
1..1
0..*
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What do classes represent
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Not all classes represent information
Other roles for classes:
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Getting input from the user and displaying output
Controlling the flow of activity while the program
runs
Other specialised tasks for example formatting
output, getting information into and out of the
database, and so on
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The GCU Adventure Game
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Simple example of a system which uses
objects which do a range of jobs and work
together as a complete program
The GCU game is a text adventure game
(interactive fiction)
Inspired by Hitchhikers’ Guide to the Galaxy
game (but not as exciting!)
Borrowed liberally from example in Barnes
and Kolling book
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Description of the game
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The game centres around characters
travelling through a world which consists of
rooms
Each room has a description
Rooms have exits which lead to other rooms
Each room can contain several items which
may be used by a character when in that
room
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Description of the game
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An item will also have a description
A player navigates through a world by typing
commands (go north, go south, quit, and so
on)
The game can be played by several players
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Objects in the game
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game – this will be an object which sets up
the game world and controls the game play
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room – this will be an object which
represents a room in the game world
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There will be only one Game object
There may be many rooms.
item – this will be an object which represents
an item in a room
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There may be several items in each room.
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Objects in the game
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description – this simply describes a room
or item
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exit – an exit from a room is really just a way
into another room
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a property rather than an object in its own right
exit is actually a way of referring to a room
object
player – this will be an object which
represents a player
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player will be in one room at any time
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Objects in the game
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There may be several players in the game.
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command – this will be an object as the job
of representing players’ actions may be quite
complicated
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Each player should have a name, which is a
property of the object.
one command object for each input entered by
a player.
Others may be required as program develops
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Model for the game
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Class diagram shows classes and properties
identified, and suggests how they may be
linked, or associated
Game
Command
Room
-description
Player
-exit
-name
Item
-description
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Importance of the class diagram
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While it is usually not the only part of a model
of a system, the class diagram is very
important when you start to build the system
as a Java program
The classes become the Java classes which
you need to write
Other diagrams are also useful, e.g. Activity,
use case, sequence
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What’s next?
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Build incrementally a working implementation
of the “World of GCU” adventure game
As we do so you will learn about some new
programming techniques and tools as they
are needed
You will also learn how the associations
between classes in the game are
implemented in Java
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