COM158 Algorithmic Programming 1 Semester 1

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COM158 Algorithmic Programming 1Semester 1

• Lecture 1 Introduction
• Week beginning 20th September 2004
• Lecturer Dr. H. Sayers
• Room MG236
• Tel 75553 (internal)
• 028 71 375553 (external)
• E-mail hm.sayers_at_ulster.ac.uk
• Web http//www.infm.ulst.ac.uk/heather

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Reading Materials

• The core text for this module is
• Tony Jenkins and Graham Hardman, How to Program
  Using Java, Palgrave Macmillan, 2004
  ISBN1-4039-1223-8
• You should purchase this book immediately as you
  will be required to read chapters from it each
  week.
• There are many other textbooks on Java which can
  be used to supplement the core text. A list of
  reading materials is available on the Module
  Handout.
• A useful Internet resource is Bruce Eckels
  Thinking in Java eBook which can be downloaded
  from http//www.mindview.net/Books/TIJ/

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Lecture Aims

• To introduce computer programming and computer
  languages
• To introduce the concept of an object-oriented
  programming language
• To introduce you to the process of problem
  analysis and designing a solution
• To introduce the BlueJ Integrated Development
  Environment (IDE)
• To introduce WebCT

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Learning Outcomes

• You should be aware of the concepts of computer
  programming and computer languages
• You should be aware of the concepts of object
  oriented computer programming
• You should be able to take a simple problem,
  analyse it, and design a solution
• You should be able to find your way around the
  BlueJ IDE and the WebCT environment

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What is a computer?

• An electronic device responding to patterns of
  electrical impulses
• 1ON 0OFF
• 2 main components
• Hardware electronic devices
• Software operating system, programs
• Aim - to simulate human intelligence
• How?
• Computer programs

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Data Meaning Information

• Program
• Data Processing
• A computer is only as intelligent as the sequence
  of instructions it uses i.e. The Program, which
  is created and entered by YOU

Information
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A Computer Program

• An algorithm presented to a computer to enable it
  to carry out some task.
• Written by a programmer in a programming language
• The programming language has a vocabulary which
  the programmer uses to write a set of
  instructions which the computer can understand
  and execute
• This set of instructions form the computer program

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Programming Languages

• There are 3 general types
• Machine Language (Binary code) - the only
  language computers can understand
• Assembly Language (Eg. LDA, ADD, STO)
• Translator programs (Assemblers) were developed
  to convert to machine language
• High Level Languages (Eg. COBOL, PASCAL, C, C,
  JAVA)
• Instructions look almost like everyday English

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Compilation

• Since a computer can only understand two symbols
  (0 or 1 (binary)), a translation mechanism is
  necessary if a programmer is to be able to
  communicate with a computer effectively
• A program is created in a text editor or an IDE
  such as BlueJ
• A program exists as a file on your computer
  system. Java files have the extension .java (e.g.
  program.java)
• At this stage, it is called the source code of
  the program

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Compilation

• The source code has to be translated into a form
  that the computer can execute it has to be
  compiled
• Translator programs compilers. They carry out
  the process of compilation
• The result of compilation is an executable file

Source Code
Executable
Compiler
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Compilation

• Carrying out the process of compilation when
  using an Integrated Development Environment such
  as BlueJ is usually a matter of clicking a button
• If the compilation process is successful, another
  file will be produced with a .class extension
• In the case of program.java, a file will be
  created called program.class this is known as
  bytecode and can be run (executed) on any
  platform using a java interpreter

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Compilation errors

• Programmers sometimes make mistakes!
• If this is the case, the program will not compile
  to produce an executable file
• The compiler will tell the programmer (as best it
  can) where or what the error is and the
  programmer must correct the error and compile
  again
• Hints for understanding your compilers error
  report
• If a long list of errors is reported, correct the
  first and recompile
• If the line where the error is identified is
  correct, look at the lines directly before it

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Running (executing) your program

• Once compiled successfully (no errors), your
  program is ready to be executed
• Running a program requires the Java Virtual
  Machine - another program which runs the
  compiled version of code (the bytecode) on the
  computer
• The JVM can also access other program code from
  various libraries on the system, known as
  packages which contain basic Java functions (They
  have to be imported into your program)
• Execution of Java code again depends on your
  computer system

Source Code
Bytecode
JVM
Compiler
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Objects

• Java is an object-oriented programming language
  and is based on the use of basic building blocks
  called objects
• An object (in the context of computer
  programming) is something that is processed or
  manipulated by the program
• Example a person there are many different
  people and each one represents an instance of the
  object type person
• Every object has attributes features that
  characterise it
• Each attribute has only one value for each object
  instance
• Each attribute has a particular type e.g. a
  persons date of birth is a number (programming
  languages support a range of different types)
• An objects attributes can themselves be objects
  (e.g. the date of birth attribute of a person
  object could be an object itself with the
  attributes of day, month and year)

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Methods

• An object may have procedures which use its
  attributes to produce particular results
  methods
• There are two types of methods
• Those which return a value, and
• Those which do not
• Take the Date example. Possible methods might be
• Find the next date
• Determine if the date is valid
• Display the date in a particular format
• Finding the next date will involve returning
  another date
• Determining if a date is valid will involve
  returning either true or false ( a boolean value)
• Displaying the date will not return any value but
  will display something on the screen

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Methods

• A method which returns some value must have a
  type known as its return type
• A method which does not return a value is known
  as a void method
• An object type is defined by ATTRIBUTES and
  METHODS
• A programmer can now use our Date object type by
  writing programs which create instances of a Date
  and use them

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Why use objects?

• Reusability program code of one object type can
  be reused in other programs which also make use
  of the object type
• Easy to build up libraries (packages) which can
  be used over and over again
• Savings in time and money

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Object-oriented programming

• Step One - look at the problem and identify the
  types of the objects needed
• Step Two - write the code for these object types
• Step Three - write the code which use the
  instances of these object types

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Step One Analysis and Design

• THE MOST IMPORTANT STEP!
• Before any program is written, it is vitally
  important that the problem is carefully analysed
  to produce a carefully designed solution
• Analysis and design are usually structured in the
  form of a formal methodology or, more informally,
  in a step-by-step approach

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A set of steps

• Identify objects the basic building blocks for
  your program
• Identify attributes and their types (this may
  lead to the identification of other objects)
• Identify methods decide what you want to be
  able to do with the object
• Design the methods each method is really a
  small program which carries out a task, and has
  to be designed separately
• Design the program this is the final program
  which makes use of the object types

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An example

• There are many students taking the module
  COM158M1 from many different courses. A program
  is required to assist with the administration of
  the module. The module coordinator wants to be
  able to keep track of all the students progress.
  She needs to know each students name, gender,
  age and course on which he/she is enrolled. When
  a student completes an assignment (of which there
  are three), she needs to record the mark achieved
  and be able to calculate an overall average mark
  ad corresponding grade (Grade D is lt40, C is
  40-50, B is 51-65, A is 66).

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Identify the objects

• Nouns within the problem description include
• Student
• Module
• Course
• Module coordinator
• Assignment
• Mark
• Grade
• Which of these nouns are needed as objects?

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Identify the objects

• Refined list
• Student
• Course
• Assignment
• Why have the others been left out of the refined
  list?
• We end up with 3 objects which we will call
  Student, Course and Assignment
• The next step is to identify the attributes for
  each object

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Identify the attributes and their types

• This can be done from the problem description,
  but is more usually done in consultation with the
  person who requires the program (in this case,
  the module coordinator)
• Student
• Name (String) Age (Number) Gender (Character
  M or F)
• Course (instance of a Course object)
• Assignment1 Assignment2Assignment3 (instances
  of an Assignment object)
• Grade
• Course
• Title (String)
• Code (String)
• Assignment
• Number (Number)
• Title (String)
• Mark (Number)

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Identify the methods

• Focus on the problem description what is the
  main focus of the final program?
• Possibilities for the Student object
• Print a description of a students personal
  details
• Calculate a students average mark
• Calculate a students grade
• Print a students average mark and grade
• Possibilities for the Course object
• Change the Course title
• Change the Course code

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Identify the methods

• Possibilities for the Assignment object
• Read in and store a mark for the assignment
• Print the assignment mark
• It is possible for an object type to have no
  methods only attributes
• It may also be the case that the module
  coordinator wants to display a list of students
  on a particular course who are taking the module,
  and calculate the average for that group of
  students
• Methods which can do this are not methods which
  belong to the object types they operate on
  collections of objects and not on individual
  objects they are carried out by the programs
  which use the objects and are implemented by the
  programmer

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Design the methods

• This is usually done in a form of pseudocode
  rather than in text (which can become quite
  complicated in a complex method), it is usually
  quite close to the programming language
• There are various styles which can be used its
  should be clear and unambiguous
• Example
• IF the average mark is 70 or above
• RETURN the value A

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Design the program

• Once the object types have been designed, the
  last design stage involves designing the program
  that will use them
• Again, this involves pseudocode
• Example
• Read in a students personal details
• Read in the assignment marks
• Print the assignment marks
• Calculate the average mark and grade
• Print the average mark and grade
• This is very high level pseudocode which needs to
  be refined into much more detail we will learn
  how to do this as we move on
• Step Two and Three (writing the code) follow on
  from design
• To be able to write the code, we first need to
  become familiar with the BlueJ IDE..

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The BlueJ Integrated Development Environment
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Steps for developing an application using the
BlueJ IDE

• Create a project (Its useful to do this each
  week)
• Set up a folder in your U directory called
  JavaPrograms and save all your projects in this
  folder (You should also make backup copies on
  floppy disk or CD)
• Create a class within your project
• Edit the class (type in your code) and save it
• Compile (Compile button on the toolbar)
• If there are errors, correct them. A message will
  appear in the area at the bottom of the window
  telling you where the errors are.
• When compiled with no errors, close the editor
• Execute the program
• NOTE There are full instructions for setting up
  and using BlueJ on my website http//www.infm.uls
  t.ac.uk/heather/lecture03.htm

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Exercises

• Essential Reading
• Chapters 1-5 of the core text (before next weeks
  lecture)
• In this weeks practical
• Print the BlueJ user guide available on the web
  and become familiar with the IDE
• Login to WebCT and become familiar with the
  environment