Collections and classes

1
Collections and classes
2
Projects in this ppt

• Collection interface practice
• The microwave oven simulator
• Bank account

3
A collection is

• Linear, like an array
• Not static, but extensible in length
• Homogeneous, but made up of key-value pairs that
  dont have to have the same data type.
• You dont always reference indices, although you
  may
• You can reference before or after
• You can get an index out of range error, as with
  an array, if you use an illegal index

4
Adding items

• Given
• Dim guys as Collection
• guys new Collection
• Then use
• mycollection.add(theItem)
• Or
• mycollection.add(theItem, keyval)
• Or
• mycollection.add(theItem, keyval,beforeguy)
• Or
• mycollection.add(theItem, keyval,,afterguy)

5
An interface to test collection
6
Suppose 9999 is added with keySpecial
7
Find entry with keySpecial
8
Code for Find button uses the collection.contains(
) method

• Private Sub btnFind_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles btnFind.Click
• Dim key As String
• key txtKey.Text
• If Guys.Contains(key) Then
• lstdisplay.Items.Add("Found")
• Else
• lstdisplay.Items.Add("Not Found")
• End If
• End Sub

9
Removing Special value
10
Adding before another key uses
collection.add(data,key,beforewhichone)

• Private Sub btnBefore_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles btnBefore.Click
• data txtData.Text
• keyVal txtKey.Text
• Dim before As String
• before txtPosition.Text
• Guys.Add(data, keyVal, before)
• Display()
• End Sub

11
Add Jim before Sue
12
Add before another key
13
Object-Oriented programming

• Object-oriented languages make abstractions and
  simplifications of real world entities which need
  to be modeled to define objects in the
  software.
• Essential features of the real-world object are
  properties of the software object.
• Essential functionality of the real-world entity
  becomes a service or method or function of the
  software entity.
• Objects have fields and methods. Fields hold
  values, methods do stuff.
• A student object might have fields name,
  address, GPA, and so on.

14
Object-Oriented programming continued

• Simple accessor and mutator methods allow a
  programmer to get or set field values of an
  object.
• Get and set are the words which are used to
  define these methods in VB, although attributes
  of a class called its properties can also be
  used to get at this information in VB
• So a student object might have a String field
  called Name, and methods getName() to retrieve
  the name and setName(toNewName) to change the
  name.
• We wont talk about these methods for quite a
  while, but in VB they are called subs and
  functions.

15
OOPbuilding your own classes in VB

• OOP refers to object-oriented programming. A
  class is a definition of an object.
• Objects are programmatic analogies to real-life
  entities.
• Objects have fields, constructors and methods.
• VB supports objects. Notice, your form is a
  class.
• A class is an instantiation of an object

16
Microwave project
17
Building a class select vb class
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Code for time class

• Public Class Time
• Dim minutes, seconds As Integer
• Public Sub New(ByVal mtmp As Integer, ByVal
  sectmp As Integer)
• minutes mtmp
• seconds sectmp
• End Sub
• Public Sub New()
• minutes 0
• seconds 0
• End Sub
• End Class

19
constructor

• Constructor for a class is New()
• Multiple constructors are allowed see previous
  slide
• Arguments passed depend on the class being
  constructed

20
Adding an instance of a class to a project
21
Getter/Setter methods (Accessor and mutator
methods)

• Accessor methods are called get
• Mutator methods are called set
• These appear in VB as properties of fields

22
Time class with minute property

• Public Class Time
• Dim minutes, seconds As Integer
• Public Sub New(ByVal mtmp As Integer, ByVal
  sectmp As Integer)
• minutes mtmp
• seconds sectmp
• End Sub
• Public Property minute() As Integer
• Get
• code goes here
• End Get
• Set(ByVal Value As Integer)
• code goes here
• End Set
• End Property
• End Class

23
Constructor setting properties

• Public Sub New(ByVal mtmp As Integer, ByVal
  sectmp As Integer)
• minute mtmp 'using type checking of
  property
• second sectmp
• End Sub

24
The entire time class

• Public Class Time
• Dim minutes, seconds As Integer
• Public Sub New(ByVal mtmp As Integer, ByVal
  sectmp As Integer)
• minute mtmp 'using type checking of
  property
• second sectmp
• End Sub
• Public Property minute() As Integer
• Get
• Return minutes
• End Get
• Set(ByVal Value As Integer)
• If Value gt0 and Value lt 60 Then
• minutes Value
• Else
• minutes 0
• End If
• End Set
• End Property
• Public Property second() As Integer

25
Timer object

• you can get a timer from the tookbox and add it
  (to your component tray)

26
Microwave, running
27
Microwave done
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Using a timer

• Be sure to enable your timer.
• Tmrclock.enabledtrue
• ' Sets the timer interval to 1 seconds.
• tmrclock.Interval 1000
• strtime "
• Be sure to start your timer
• Tmrclock.start()
• In the microwave example, the timer needs to be
  reset when they press the start button.

29
The clock tick sub

• Private Sub tmrClock_Tick(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles tmrclock.Tick
• If timeobj.second gt 0 Then
• timeobj.second - 1
• ElseIf timeobj.minute gt 0 Then
• timeobj.minute - 1
• timeobj.second 59
• Else
• tmrclock.Enabled False
• Beep()
• Lbl.Text "done"
• pnl.BackColor Color.Black
• Return
• End If
• Lbl.Text String.Format("0d21d2",
  timeobj.minute, timeobj.second)
• End Sub

30
Display time sub

• Sub displayTime()
• Dim intsec, intmin As Integer
• Dim strdisplay As String
• If strtime.length gt 4 Then
• strtime strtime.substring(0, 4)
• End If
• strdisplay strtime.padleft(4,
  convert.tochar("0"))
• intsec Convert.ToInt32(strdisplay.Substr
  ing(2))
• intmin Convert.ToInt32(strdisplay.Substr
  ing(0, 2))
• timeobj New Time(intmin, intsec)
• Lbl.Text String.Format("0D21D2",
  intmin, intsec)
• End Sub

31
Start button

• Private Sub start_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles start.Click
• Dim intsec As Integer
• Dim intmin As Integer
• strtime strtime.PadLeft(4,
  Convert.ToChar("0"))
• intsec Convert.ToInt32(strtime.substring
  (2))
• intmin Convert.ToInt32(strtime.Substring
  (0, 2))
• timeobj New Time(intmin, intsec)
• Lbl.Text String.Format("0d21d2",
  timeobj.minute, timeobj.second)
• strtime ""
• tmrClock.enabled True
• pnl.BackColor Color.Yellow
• End Sub

32
Clear button

• Private Sub clear_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles clear.Click
• Lbl.Text "Microwave"
• strtime ""
• timeobj New Time(0, 0)
• tmrClock.enabled False
• pnl.BackColor Color.Black
• End Sub

33
A button click

• Private Sub Btn1_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles Btn1.Click
• Beep()
• strtime "1"
• displayTime()
• End Sub

34
A sort of bank account project
35
Button events

• First and last buttons display respectively the
  customers who are first and last in the customer
  array
• Next displays the next customer and previous
  displays the previous customer

36
The account class

• Public Class Account
• Dim first, last, middle As String
• Dim balance As Double
• Dim accountnum As String
• constructor sets name fields, balance and
  account number info
• Public Sub New(ByVal ftmp As String, ByVal mtmp
  As String, ByVal ltmp As String, ByVal bal As
  Double, ByVal acct As String)
• firstName ftmp
• midName mtmp
• lastName ltmp
• acctBalance bal
• accountNumber acct
• End Sub
• Public Property firstName() As String
• Get
• Return first
• End Get
• Set(ByVal ftmp As String)
• first ftmp
• End Set

37
Account class continued

• Public Property midName() As String
• Get
• Return middle
• End Get
• Set(ByVal ftmp As String)
• middle ftmp
• End Set
• End Property
• Public Property lastName() As String
• Get
• Return last
• End Get
• Set(ByVal ftmp As String)
• last ftmp
• End Set
• End Property
• Public Property acctBalance() As Double
• Get
• Return balance

38
Bank proj uses an array of accounts

• Dim customers As Account()
• Const num 20
• Dim current As Integer -1

39
accounts

• Dim i As Integer
• For i 1 To num
• customers(i) New Account("bob" i,
  "micky" i, "jones" i, 1.0, "0" i "0" i)
• Next

40
The set button sets current customer fields to
updated content
41
Revisiting this entry shows updated data
42
The get button

• Get button should take a last name or account
  number and display that persons information

43
Data is retrieved
44
One of the two lookup functions

• Private Function lookupName(ByVal last As
  String) As Integer
• Dim temp As Integer 0
• Dim j As Integer
• For j 1 To num
• If last customers(j).lastName Then
• temp j
• End If
• Next
• lookupName temp
• End Function

45
Optional arguments

• There are ways to get around writing two
  different lookup functions, one for a last name
  and one for an account number.
• We could send either last name or account number
  along with a control parameter (1lastname
  supplied, 2 accountnumber supplied)
• C and VB allow optional arguments to be passed.
  It doesnt save a lot of work, but a later slide
  shows the code with optional arguments.

46
Preparing to look for a name
47
Customer is found by last name or acct
48
Code for get button

• Private Sub btnGet_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles btnGet.Click
• Dim find As Integer
• If txtLast.Text "" And txtAccount.Text
  "" Then
• MessageBox.Show("you must enter name
  or account number", "data entry error",
  MessageBoxButtons.OK, MessageBoxIcon.Error)
• Return
• Else
• If txtLast.Text "" Then
• find lookup(, txtAccount.Text)
• Else
• find lookup(txtLast.Text, )
• End If
• If find lt 1 Then
• MessageBox.Show("you must enter
  valid name or account number", "data entry
  error", MessageBoxButtons.OK, MessageBoxIcon.Error
  )
• Else
• current find
• display()
• End If
• End If
• End Sub