Transcript Programming - De Montfort University

Objects Methods and Instantiation
Programming
Programming is the act of writing instructions that tell a computer
how to do something.
This module is a starting point into a huge topic
You will almost certainly not get this on the first attempt
I assume no prior knowledge of programming
In this first lecture we will consider…
 How we may use a system of notation to control computer
technology
 How objects may be used to represent and control computer
technology via methods and properties
 The relationship between an object and a class and how
instantiation creates an object from a class
Sending a Simple Instruction to a
Computer
I want the computer to shut down
How would I do this?
(Use of my senses)
How would I tell one of you to do it?
(Use of natural language)
How do we tell the computer to turn itself off?
Natural Language and Computers
“ok computer turn your self off now”
 Does the computer understand the words we have used?
 Strong regional accents?
 Consider the following…
 Off computer turn now
 OK puter turn thesel ov now
 Cmptr trn yrslf ff nw
 Natural language allows for ambiguity and imprecision
 Computers are really quite thick
Computer Programming and
Music
 Parallels may be drawn between programming a
computer and playing an instrument.
 (It is my observation that many programmers are also
musicians)
 With music we have the same problem as with a
computer
 How do we tell the instrument / musician what it is we
want to hear?
What is this?
Add the words…
Music Notation as a Program
 Once you understand the rules you may create / play
music of varying complexity
 The same tune may be reproduced on different
instruments
 The basic rules are very simple
 The staff indicates the pitch of the sound…
 The shape of the notes tell us how long they should be played
for…
 Sequence matters!
Symbols and Meaning
 We use symbols all of the time in our daily life
 “Represents” the tune “three blind mice” but it isn’t the tune
De Montfort University
The Gateway
Leicester
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 Represents the address but it isn’t the place
Understanding the Symbols
 Understanding the symbols is the first problem you
will face in learning how to program
Which Code is Correct?
Dim MyAge As Integer
MyAge = 23
If MyAge > 21 Then
lblError-Text = "You are old enough"
End If
Or…
Dim MyAge As Integer
MyAge = 23
If MyAge > 21 Then
lblError.Text = "You are old enough"
End If
Computer Programming
We want to create:
 A system that accurately identifies the individual
components in a computer so we may control them
 A system that may be used to set the sequence of
instructions such that they are carried out in the way we
intend
 A system of representation that is easy to maintain
avoiding unnecessary duplication and excess baggage
 Something that is reasonably easy for us as human
beings to write and understand (we don’t want the
symbols to get in the way of the meaning)
Objects, Classes, Methods,
Properties and Instantiation
 Lots of new terms to understand
 Objects provide tools for referencing and controlling
bits of the computer
 Classes are the “recipes” that define objects
 Methods tell objects to do something
 Properties control the settings of an object
 Instantiation is the act of making an object out of a class
Cuba the Cat - Properties
Legs
Tails
Ears
Fangs
4
1
2
3
Properties tell us
how the object
is set up
Cuba the Cat - Methods
Release - let Cuba
outside
Feed - give Cuba
some food
Scoop - clean up
after Cuba
 Methods make
the object do
something
The Computer as an Object




Properties and methods not about Cats
We want to represent and control the computer
View the computer system as a set of objects
We may think of the computer expressed as an object
MyComputer.TurnOff()
 MyComputer represents the entire computer
 TurnOff is a method that turns the computer off
 Starting to develop a system of notation rather like musical
notation
Classes
 Classes contain the code defining an object
Instantiation
 Takes the recipe contained in the class and makes an
object we may use
The Computer System
 We will be looking at a range of objects and classes
allowing us to control different parts of the computer
system
 The screen (buttons, text boxes and lists)
 The RAM (variables)
 A Database (DataConnection class)
 + others
 Also look at control structures (assignment, functions,
loops, if statements)
The Three Layer Architecture
Overview
 Don’t get bogged down in the detail!
Programming is the act of writing instructions that tell
a computer how to do something
We need a standard system of notation allowing us to
represent what the computer is to do that makes
reasonable sense to human beings
Important Key Concepts
Object
Method
Property
Class
Instantiation
A way of representing computer
technology so that we may control it
Used to tell an object to do
something
Used to find out or control
something out about the object
The definition for an object
The process of making an object
from a class
Computer System Split into Layers
 The Presentation Layer – the part the user interacts
with
 The Middle Layer – containing classes allowing us to
do things
 The Data Layer – where are database is stored
Finally…
There is one final way in which programming is like music!
Both require constant hands-on practise!
You must do the work!
You will not learn how to program on the first second or third
attempt
You must practise and refine your skills