オブジェクト指向の基本的効用について、プリミティブな状態から順に見ていきましょう。
Practice1 「バラバラのデータ」
人について、属性{ ID、Name、Birthday }を扱うとします。
このサンプルでは、4行目から9行目までに扱う人数×属性数分の変数を定義しています。
いうまでもなく、これではコーディングが大変ですし、応用が利きません。
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Public Sub Practice1() |
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Dim ID_1 As Integer = 1 |
Dim Name_1 As String = "Satohru" |
Dim Birthday_1 As Date = #5/25/1967# |
Dim ID_2 As Integer = 2 |
Dim Name_2 As String = "Ayase" |
Dim Birthday_2 As Date = #3/24/1985# |
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Dim Message As String = |
"登録者は、" & Name_1 & "と" & Name_2 & "です。" |
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MessageBox.Show("Practice1" & vbCrLf & Message) |
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End Sub |
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Practice2 「データの構造化」
このサンプルでは、構造体を用いて「バラバラのデータ」を構造化しています。
Practice1より理解しやすいプログラムになり、間違いが起こりにくそうです。
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Private Structure PersonStructure |
Friend ID As Integer |
Friend Name As String |
Friend Birthday As Date |
End Structure |
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Public Sub Practice2() |
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Dim Person1, Person2 As PersonStructure |
With Person1 |
.ID = 1 |
.Name = "Satohru" |
.Birthday = #5/25/1967# |
End With |
With Person2 |
.ID = 2 |
.Name = "Ayase" |
.Birthday = #3/24/1985# |
End With |
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Dim Message As String = |
"登録者は、" & Person1.Name & "と" & |
Person2.Name & "です。" |
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MessageBox.Show("Practice2" & vbCrLf & Message) |
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End Sub |
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Practice3 「構造化されたデータを束ねる」
次は、構造体の配列を3行目で定義しました。
このように構造化されたデータを配列に束ねることによって、
16行目のループ処理によってシステマチックなデータ処理が可能になります。
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Public Sub Practice3() |
Dim Persons(1) As PersonStructure |
With Persons(0) |
.ID = 1 |
.Name = "Satohru" |
.Birthday = #5/25/1967# |
End With |
With Persons(1) |
.ID = 2 |
.Name = "Ayase" |
.Birthday = #3/24/1985# |
End With |
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Dim Message As String = "" |
For i = 0 To Persons.Length - 1 |
Message &= vbCrLf & Persons(i).Name |
Next |
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Message = "登録者は、" & Message & "です。" |
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MessageBox.Show("Practice3" & vbCrLf & Message) |
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End Sub |
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Practice4 「構造化されたデータに振る舞いを加える」
生年月日から年齢を求めたい。そんな時に Person.Age とコーディングできたら便利です。
そこで、次のようなPersonClassを作ります。
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Friend Class PersonClass |
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Private m_ID As Integer |
Private m_Name As String |
Private m_Birthday As Date |
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Friend Property ID() As Integer |
Get |
Return m_ID |
End Get |
Set(ByVal value As Integer) |
m_ID = value |
End Set |
End Property |
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Friend Property Name() As String |
Get |
Return m_Name |
End Get |
Set(ByVal value As String) |
m_Name = value |
End Set |
End Property |
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Friend Property Birthday() As Date |
Get |
Return m_Birthday |
End Get |
Set(ByVal value As Date) |
m_Birthday = value |
End Set |
End Property |
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Friend ReadOnly Property Age() As Integer |
Get |
Dim _year As Integer = |
CType(Today.ToString("yyyy"), Integer) |
Dim _MMdd As Integer = |
CType(Today.ToString("MMdd"), Integer) |
Dim _birthYear As Integer = |
CType(m_Birthday.ToString("yyyy"), Integer) |
Dim _birthMMdd As Integer = |
CType(m_Birthday.ToString("MMdd"), Integer) |
Dim _age As Integer = _year - _birthYear |
If _MMdd < _birthMMdd Then |
_age = _age - 1 |
End If |
Return _age |
End Get |
End Property |
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End Class |
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下記コードのように、
構造体では実現できなかった振る舞いをクラスは実現してくれます。
＊上記取り消し線部分が間違っていましたので、訂正記事を掲載しました。
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Public Sub Practice4() |
Dim oPerson1 As New PersonClass With { |
.ID = 1, |
.Name = "Satohru", |
.Birthday = #5/25/1967#} |
Dim oPerson2 As New PersonClass With { |
.ID = 2, |
.Name = "Ayase", |
.Birthday = #3/24/1985#} |
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Dim Message As String = |
oPerson1.Name & "の年齢は、" & |
oPerson1.Age.ToString & "歳です。" & |
vbCrLf & |
oPerson2.Name & "の年齢は、" & |
oPerson2.Age.ToString & "歳です。" |
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MessageBox.Show("Practice4" & vbCrLf & Message) |
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End Sub |
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Practice5 「クラスを束ねるとさらに便利に」
PersonClassのインスタンスを13行目でコレクションクラスに追加しています。
＊Public Sub Practice5()を含むクラスは、System.Collections.CollectionBaseを継承しています。
これにより For Each（19行目） やLINQ（27行目）により、より一層データを便利に扱うことができます。
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Public Sub Practice5() |
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Dim oPerson1 As New PersonClass With { |
.ID = 1, |
.Name = "Satohru", |
.Birthday = #5/25/1967#} |
Dim oPerson2 As New PersonClass With { |
.ID = 2, |
.Name = "Ayase", |
.Birthday = #3/24/1985#} |
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With List |
.Add(oPerson1) |
.Add(oPerson2) |
End With |
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Dim Message As String = "" |
For Each v As PersonClass In List |
Message &= vbCrLf & v.Name |
Next |
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Message = "登録者は、" & Message & "です。" |
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MessageBox.Show("Practice5-1" & vbCrLf & Message) |
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Dim rs = From v As PersonClass In List Select v.Age |
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Message = |
"登録者は" & rs.Count & "名で、" & |
"平均年齢は、" & rs.Average & "歳です。" |
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MessageBox.Show("Practice5-2" & vbCrLf & Message) |
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End Sub |
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全体は下記のようにコーディングされています。
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Public Class Sample |
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Inherits System.Collections.CollectionBase |
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Public Sub Practice1() |
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Dim ID_1 As Integer = 1 |
Dim Name_1 As String = "Satohru" |
Dim Birthday_1 As Date = #5/25/1967# |
Dim ID_2 As Integer = 2 |
Dim Name_2 As String = "Ayase" |
Dim Birthday_2 As Date = #3/24/1985# |
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Dim Message As String = |
"登録者は、" & Name_1 & "と" & Name_2 & "です。" |
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MessageBox.Show("Practice1" & vbCrLf & Message) |
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End Sub |
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Private Structure PersonStructure |
Friend ID As Integer |
Friend Name As String |
Friend Birthday As Date |
End Structure |
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Public Sub Practice2() |
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Dim Person1, Person2 As PersonStructure |
With Person1 |
.ID = 1 |
.Name = "Satohru" |
.Birthday = #5/25/1967# |
End With |
With Person2 |
.ID = 2 |
.Name = "Ayase" |
.Birthday = #3/24/1985# |
End With |
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Dim Message As String = |
"登録者は、" & Person1.Name & "と" & |
Person2.Name & "です。" |
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MessageBox.Show("Practice2" & vbCrLf & Message) |
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End Sub |
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Public Sub Practice3() |
Dim Persons(1) As PersonStructure |
With Persons(0) |
.ID = 1 |
.Name = "Satohru" |
.Birthday = #5/25/1967# |
End With |
With Persons(1) |
.ID = 2 |
.Name = "Ayase" |
.Birthday = #3/24/1985# |
End With |
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Dim Message As String = "" |
For i = 0 To Persons.Length - 1 |
Message &= vbCrLf & Persons(i).Name |
Next |
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Message = "登録者は、" & Message & "です。" |
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MessageBox.Show("Practice3" & vbCrLf & Message) |
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End Sub |
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Public Sub Practice4() |
Dim oPerson1 As New PersonClass With { |
.ID = 1, |
.Name = "Satohru", |
.Birthday = #5/25/1967#} |
Dim oPerson2 As New PersonClass With { |
.ID = 2, |
.Name = "Ayase", |
.Birthday = #3/24/1985#} |
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Dim Message As String = |
oPerson1.Name & "の年齢は、" & |
oPerson1.Age.ToString & "歳です。" & |
vbCrLf & |
oPerson2.Name & "の年齢は、" & |
oPerson2.Age.ToString & "歳です。" |
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MessageBox.Show("Practice4" & vbCrLf & Message) |
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End Sub |
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Public Sub Practice5() |
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Dim oPerson1 As New PersonClass With { |
.ID = 1, |
.Name = "Satohru", |
.Birthday = #5/25/1967#} |
Dim oPerson2 As New PersonClass With { |
.ID = 2, |
.Name = "Ayase", |
.Birthday = #3/24/1985#} |
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With List |
.Add(oPerson1) |
.Add(oPerson2) |
End With |
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Dim Message As String = "" |
For Each v As PersonClass In List |
Message &= vbCrLf & v.Name |
Next |
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Message = "登録者は、" & Message & "です。" |
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MessageBox.Show("Practice5-1" & vbCrLf & Message) |
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Dim rs = From v As PersonClass In List Select v.Age |
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Message = |
"登録者は" & rs.Count & "名で、" & |
"平均年齢は、" & rs.Average & "歳です。" |
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MessageBox.Show("Practice5-2" & vbCrLf & Message) |
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End Sub |
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End Class |
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Friend Class PersonClass |
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Private m_ID As Integer |
Private m_Name As String |
Private m_Birthday As Date |
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Friend Property ID() As Integer |
Get |
Return m_ID |
End Get |
Set(ByVal value As Integer) |
m_ID = value |
End Set |
End Property |
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Friend Property Name() As String |
Get |
Return m_Name |
End Get |
Set(ByVal value As String) |
m_Name = value |
End Set |
End Property |
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Friend Property Birthday() As Date |
Get |
Return m_Birthday |
End Get |
Set(ByVal value As Date) |
m_Birthday = value |
End Set |
End Property |
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Friend ReadOnly Property Age() As Integer |
Get |
Dim _year As Integer = |
CType(Today.ToString("yyyy"), Integer) |
Dim _MMdd As Integer = |
CType(Today.ToString("MMdd"), Integer) |
Dim _birthYear As Integer = |
CType(m_Birthday.ToString("yyyy"), Integer) |
Dim _birthMMdd As Integer = |
CType(m_Birthday.ToString("MMdd"), Integer) |
Dim _age As Integer = _year - _birthYear |
If _MMdd < _birthMMdd Then |
_age = _age - 1 |
End If |
Return _age |
End Get |
End Property |
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End Class |
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