ArrayList.TrimToSize メソッドとは？ わかりやすく解説

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ArrayList.TrimToSize メソッド

容量を ArrayList 内にある実際の要素数に設定します。

名前空間: System.Collections
アセンブリ: mscorlib (mscorlib.dll 内)
構文構文

Visual Basic (宣言)
Public Overridable Sub TrimToSize
Visual Basic (使用法)
Dim instance As ArrayList

instance.TrimToSize
C#
public virtual void TrimToSize ()
C++
public:
virtual void TrimToSize ()
J#
public void TrimToSize ()
JScript
public function TrimToSize ()
例外例外
例外の種類条件

NotSupportedException

ArrayList は読み取り専用です。

または

ArrayList が固定サイズです。

解説解説

今後コレクションに要素が追加されないことがわかっている場合は、このメソッドを使用して、コレクションのメモリ オーバーヘッドを最小化できます。

ArrayList を初期状態にリセットするには、TrimToSize の前に、Clear を呼び出します。空の ArrayList をトリムすると、ArrayList の容量は既定値に設定されます。

このメソッドは O(n) 操作です。ここで、n は Count です。

使用例使用例

ArrayList の未使用部分をなくす方法と、ArrayList の値を消去する方法を次のコード例に示します。

Visual Basic
Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Class SamplesArrayList    
    
    Public Shared Sub Main()
        
        ' Creates and initializes a new ArrayList.
        Dim myAL As New
 ArrayList()
        myAL.Add("The")
        myAL.Add("quick")
        myAL.Add("brown")
        myAL.Add("fox")
        myAL.Add("jumped")
        
        ' Displays the count, capacity and values of the ArrayList.
        Console.WriteLine("Initially,")
        Console.WriteLine("   Count    : {0}", myAL.Count)
        Console.WriteLine("   Capacity : {0}", myAL.Capacity)
        Console.Write("   Values:")
        PrintValues(myAL)
        
        ' Trim the ArrayList.
        myAL.TrimToSize()
        
        ' Displays the count, capacity and values of the ArrayList.
        Console.WriteLine("After TrimToSize,")
        Console.WriteLine("   Count    : {0}", myAL.Count)
        Console.WriteLine("   Capacity : {0}", myAL.Capacity)
        Console.Write("   Values:")
        PrintValues(myAL)
        
        ' Clear the ArrayList.
        myAL.Clear()
        
        ' Displays the count, capacity and values of the ArrayList.
        Console.WriteLine("After Clear,")
        Console.WriteLine("   Count    : {0}", myAL.Count)
        Console.WriteLine("   Capacity : {0}", myAL.Capacity)
        Console.Write("   Values:")
        PrintValues(myAL)
        
        ' Trim the ArrayList again.
        myAL.TrimToSize()
        
        ' Displays the count, capacity and values of the ArrayList.
        Console.WriteLine("After the second TrimToSize,")
        Console.WriteLine("   Count    : {0}", myAL.Count)
        Console.WriteLine("   Capacity : {0}", myAL.Capacity)
        Console.Write("   Values:")
        PrintValues(myAL)
    End Sub

    Public Shared Sub PrintValues(myList
 As IEnumerable)
        Dim obj As [Object]
        For Each obj In
  myList
            Console.Write("   {0}", obj)
        Next obj
        Console.WriteLine()
    End Sub 'PrintValues

End Class

' This code produces the following output.
' 
' Initially,
'    Count    : 5
'    Capacity : 16
'    Values:    The    quick    brown    fox    jumped
' After TrimToSize,
'    Count    : 5
'    Capacity : 5
'    Values:    The    quick    brown    fox    jumped
' After Clear,
'    Count    : 0
'    Capacity : 5
'    Values:
' After the second TrimToSize,
'    Count    : 0
'    Capacity : 16
'    Values:
C#
using System;
using System.Collections;
public class SamplesArrayList  {

   public static void Main()
  {

      // Creates and initializes a new ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add( "The" );
      myAL.Add( "quick" );
      myAL.Add( "brown" );
      myAL.Add( "fox" );
      myAL.Add( "jumped" );

      // Displays the count, capacity and values of the ArrayList.
      Console.WriteLine( "Initially," );
      Console.WriteLine( "   Count    : {0}", myAL.Count );
      Console.WriteLine( "   Capacity : {0}", myAL.Capacity );
      Console.Write( "   Values:" );
      PrintValues( myAL );

      // Trim the ArrayList.
      myAL.TrimToSize();

      // Displays the count, capacity and values of the ArrayList.
      Console.WriteLine( "After TrimToSize," );
      Console.WriteLine( "   Count    : {0}", myAL.Count );
      Console.WriteLine( "   Capacity : {0}", myAL.Capacity );
      Console.Write( "   Values:" );
      PrintValues( myAL );

      // Clear the ArrayList.
      myAL.Clear();

      // Displays the count, capacity and values of the ArrayList.
      Console.WriteLine( "After Clear," );
      Console.WriteLine( "   Count    : {0}", myAL.Count );
      Console.WriteLine( "   Capacity : {0}", myAL.Capacity );
      Console.Write( "   Values:" );
      PrintValues( myAL );

      // Trim the ArrayList again.
      myAL.TrimToSize();

      // Displays the count, capacity and values of the ArrayList.
      Console.WriteLine( "After the second TrimToSize," );
      Console.WriteLine( "   Count    : {0}", myAL.Count );
      Console.WriteLine( "   Capacity : {0}", myAL.Capacity );
      Console.Write( "   Values:" );
      PrintValues( myAL );
   }

   public static void PrintValues(
 IEnumerable myList )  {
      foreach ( Object obj in myList )
         Console.Write( "   {0}", obj );
      Console.WriteLine();
   }

}
/* 
This code produces the following output.

Initially,
   Count    : 5
   Capacity : 16
   Values:    The    quick    brown    fox    jumped
After TrimToSize,
   Count    : 5
   Capacity : 5
   Values:    The    quick    brown    fox    jumped
After Clear,
   Count    : 0
   Capacity : 5
   Values:
After the second TrimToSize,
   Count    : 0
   Capacity : 16
   Values:
*/
C++
using namespace System;
using namespace System::Collections;
void PrintValues( IEnumerable^ myList );
int main()
{
   
   // Creates and initializes a new ArrayList.
   ArrayList^ myAL = gcnew ArrayList;
   myAL->Add( "The" );
   myAL->Add( "quick" );
   myAL->Add( "brown" );
   myAL->Add( "fox" );
   myAL->Add( "jumped" );
   
   // Displays the count, capacity and values of the ArrayList.
   Console::WriteLine( "Initially," );
   Console::WriteLine( "   Count    : {0}", myAL->Count );
   Console::WriteLine( "   Capacity : {0}", myAL->Capacity );
   Console::Write( "   Values:" );
   PrintValues( myAL );
   
   // Trim the ArrayList.
   myAL->TrimToSize();
   
   // Displays the count, capacity and values of the ArrayList.
   Console::WriteLine( "After TrimToSize," );
   Console::WriteLine( "   Count    : {0}", myAL->Count );
   Console::WriteLine( "   Capacity : {0}", myAL->Capacity );
   Console::Write( "   Values:" );
   PrintValues( myAL );
   
   // Clear the ArrayList.
   myAL->Clear();
   
   // Displays the count, capacity and values of the ArrayList.
   Console::WriteLine( "After Clear," );
   Console::WriteLine( "   Count    : {0}", myAL->Count );
   Console::WriteLine( "   Capacity : {0}", myAL->Capacity );
   Console::Write( "   Values:" );
   PrintValues( myAL );
   
   // Trim the ArrayList again.
   myAL->TrimToSize();
   
   // Displays the count, capacity and values of the ArrayList.
   Console::WriteLine( "After the second TrimToSize," );
   Console::WriteLine( "   Count    : {0}", myAL->Count );
   Console::WriteLine( "   Capacity : {0}", myAL->Capacity );
   Console::Write( "   Values:" );
   PrintValues( myAL );
}

void PrintValues( IEnumerable^ myList )
{
   IEnumerator^ myEnum = myList->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      Object^ obj = safe_cast<Object^>(myEnum->Current);
      Console::Write( "   {0}", obj );
   }

   Console::WriteLine();
}

/* 
 This code produces the following output.
 
 Initially,
    Count    : 5
    Capacity : 16
    Values:    The    quick    brown    fox    jumped
 After TrimToSize,
    Count    : 5
    Capacity : 5
    Values:    The    quick    brown    fox    jumped
 After Clear,
    Count    : 0
    Capacity : 5
    Values:
 After the second TrimToSize,
    Count    : 0
    Capacity : 16
    Values:
 */
J#
import System.*;
import System.Collections.*;

public class SamplesArrayList
{
    public static void main(String[]
 args)
    {
        // Creates and initializes a new ArrayList.
        ArrayList myAL = new ArrayList();

        myAL.Add("The");
        myAL.Add("quick");
        myAL.Add("brown");
        myAL.Add("fox");
        myAL.Add("jumped");

        // Displays the count, capacity and values of the ArrayList.
        Console.WriteLine("Initially,");
        Console.WriteLine("   Count    : {0}", (Int32)myAL.get_Count());
        Console.WriteLine("   Capacity : {0}", (Int32)myAL.get_Capacity());
        Console.Write("   Values:");
        PrintValues(myAL);

        // Trim the ArrayList.
        myAL.TrimToSize();

        // Displays the count, capacity and values of the ArrayList.
        Console.WriteLine("After TrimToSize,");
        Console.WriteLine("   Count    : {0}", (Int32)myAL.get_Count());
        Console.WriteLine("   Capacity : {0}", (Int32)myAL.get_Capacity());
        Console.Write("   Values:");
        PrintValues(myAL);

        // Clear the ArrayList.
        myAL.Clear();

        // Displays the count, capacity and values of the ArrayList.
        Console.WriteLine("After Clear,");
        Console.WriteLine("   Count    : {0}", (Int32)myAL.get_Count());
        Console.WriteLine("   Capacity : {0}", (Int32)myAL.get_Capacity());
        Console.Write("   Values:");
        PrintValues(myAL);

        // Trim the ArrayList again.
        myAL.TrimToSize();

        // Displays the count, capacity and values of the ArrayList.
        Console.WriteLine("After the second TrimToSize,");
        Console.WriteLine("   Count    : {0}", (Int32)myAL.get_Count());
        Console.WriteLine("   Capacity : {0}", (Int32)myAL.get_Capacity());
        Console.Write("   Values:");
        PrintValues(myAL);
    } //main

    public static void PrintValues(IEnumerable
 myList)
    {
        IEnumerator objMyEnum = myList.GetEnumerator();
        while (objMyEnum.MoveNext()) {
            Object obj = objMyEnum.get_Current();
            Console.Write("   {0}", obj);
        }
        Console.WriteLine();
    } //PrintValues
} //SamplesArrayList 
/* 
 This code produces the following output.
 
 Initially,
    Count    : 5
    Capacity : 16
    Values:    The    quick    brown    fox    jumped
 After TrimToSize,
    Count    : 5
    Capacity : 5
    Values:    The    quick    brown    fox    jumped
 After Clear,
    Count    : 0
    Capacity : 5
    Values:
 After the second TrimToSize,
    Count    : 0
    Capacity : 16
    Values:
 */
JScript
import System;
import System.Collections;


// Creates and initializes a new ArrayList.
var myAL : ArrayList = new ArrayList();
myAL.Add( "The" );
myAL.Add( "quick" );
myAL.Add( "brown" );
myAL.Add( "fox" );
myAL.Add( "jumped" );

// Displays the count, capacity and values of the ArrayList.
Console.WriteLine( "Initially," );
Console.WriteLine( "   Count    : {0}", myAL.Count );
Console.WriteLine( "   Capacity : {0}", myAL.Capacity );
Console.Write( "   Values:" );
PrintValues( myAL );

// Trim the ArrayList.
myAL.TrimToSize();

// Displays the count, capacity and values of the ArrayList.
Console.WriteLine( "After TrimToSize," );
Console.WriteLine( "   Count    : {0}", myAL.Count );
Console.WriteLine( "   Capacity : {0}", myAL.Capacity );
Console.Write( "   Values:" );
PrintValues( myAL );

// Clear the ArrayList.
myAL.Clear();

// Displays the count, capacity and values of the ArrayList.
Console.WriteLine( "After Clear," );
Console.WriteLine( "   Count    : {0}", myAL.Count );
Console.WriteLine( "   Capacity : {0}", myAL.Capacity );
Console.Write( "   Values:" );
PrintValues( myAL );

// Trim the ArrayList again.
myAL.TrimToSize();

// Displays the count, capacity and values of the ArrayList.
Console.WriteLine( "After the second TrimToSize," );
Console.WriteLine( "   Count    : {0}", myAL.Count );
Console.WriteLine( "   Capacity : {0}", myAL.Capacity );
Console.Write( "   Values:" );
PrintValues( myAL );
 
function PrintValues( myList : IEnumerable)  {
   var myEnumerator : System.Collections.IEnumerator  = myList.GetEnumerator();
   while ( myEnumerator.MoveNext() )
      Console.Write( "\t{0}", myEnumerator.Current );
   Console.WriteLine();
}
 /* 
 This code produces the following output.
 
 Initially,
    Count    : 5
    Capacity : 16
    Values:    The    quick    brown    fox    jumped
 After TrimToSize,
    Count    : 5
    Capacity : 5
    Values:    The    quick    brown    fox    jumped
 After Clear,
    Count    : 0
    Capacity : 5
    Values:
 After the second TrimToSize,
    Count    : 0
    Capacity : 16
    Values:
 */
プラットフォームプラットフォーム

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

開発プラットフォームの中には、.NET Framework によってサポートされていないバージョンがあります。サポートされているバージョンについては、「システム要件」を参照してください。

バージョン情報バージョン情報
.NET Framework
サポート対象 : 2.0、1.1、1.0
.NET Compact Framework
サポート対象 : 2.0、1.0
参照参照
関連項目
ArrayList クラス
ArrayList メンバ
System.Collections 名前空間
Clear
Capacity
Count

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