M1G413283 Introduction to Programming 2

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M1G413283Introduction to Programming 2

• 1. Designing a program

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Teaching staff

• Jim Paterson Room M628James.Paterson_at_gcu.ac.uk
• Katrin HartmannRoom 611

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Online resources

• Blackboard
• Announcements
• Assessment information
• Course website
• 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

• No set text notes will be provided
• The following books are recommended as additional
  reading
• 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

• Class test
• Lab exercises
• PeerWise

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Models in software development

• 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

• A Java program can be
• 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

• User interface can be
• Windows application
• Web pages
• Web page applets
• Phone applications
• Games
• Embedded
• Command line
• etc...

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Object-oriented programs

• 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

• 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

• A class specifies the following for the objects
  it is used to create
• 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

• 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?

• Information
• May be information which needs to be stored
  permanently - database

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What do classes represent

• Not all classes represent information
• Other roles for classes
• 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

• 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

• 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

• 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

• game this will be an object which sets up the
  game world and controls the game play
• There will be only one Game object
• room this will be an object which represents a
  room in the game world
• There may be many rooms.
• item this will be an object which represents an
  item in a room
• There may be several items in each room.

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Objects in the game

• description this simply describes a room or
  item
• a property rather than an object in its own right
• exit an exit from a room is really just a way
  into another room
• exit is actually a way of referring to a room
  object
• player this will be an object which represents
  a player
• player will be in one room at any time

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Objects in the game

• There may be several players in the game.
• Each player should have a name, which is a
  property of the object.
• command this will be an object as the job of
  representing players actions may be quite
  complicated
• 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

• Class diagram shows classes and properties
  identified, and suggests how they may be linked,
  or associated

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Importance of the class diagram

• 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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Whats next?

• 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