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Random Constructor (Int32)

Updated: March 2012

Initializes a new instance of the Random class, using the specified seed value.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Sub New ( _
	Seed As Integer _
)
'Usage
Dim Seed As Integer 

Dim instance As New Random(Seed)

Parameters

Seed
Type: System.Int32

A number used to calculate a starting value for the pseudo-random number sequence. If a negative number is specified, the absolute value of the number is used.

ExceptionCondition
OverflowException

Seed is Int32.MinValue, which causes an overflow when its absolute value is calculated.

Providing an identical seed value to different Random objects causes each instance to produce identical sequences of random numbers.

If your application requires different random number sequences, invoke this constructor repeatedly with different seed values. One way to produce a unique seed value is to make it time-dependent. For example, derive the seed value from the system clock. However, the system clock might not have sufficient resolution to provide different invocations of this constructor with a different seed value. This results in random number generators that generate identical sequences of pseudo-random numbers, as illustrated by the first two Random objects in the following example. To prevent this, apply an algorithm to differentiate the seed value in each invocation, or call the Thread.Sleep method to ensure that you provide each constructor with a different seed value.

Imports System.Threading

Module RandomNumbers
   Public Sub Main()
      Dim rand1 As New Random(CInt(Date.Now.Ticks And &h0000FFFF))
      Dim rand2 As New Random(CInt(Date.Now.Ticks And &h0000FFFF))
      Thread.Sleep(20)
      Dim rand3 As New Random(CInt(Date.Now.Ticks And &h0000FFFF))
      ShowRandomNumbers(rand1)
      ShowRandomNumbers(rand2)
      ShowRandomNumbers(rand3)
   End Sub 

   Private Sub ShowRandomNumbers(rand As Random)
      Console.WriteLine()
      Dim values(4) As Byte
      rand.NextBytes(values)
      For Each value As Byte In values
         Console.Write("{0, 5}", value)
      Next      
      Console.WriteLine() 
   End Sub 
End Module 
' The example displays output similar to the following: 
'      145  214  177  134  173 
'     
'      145  214  177  134  173 
'     
'      126  185  175  249  157

The following example creates Random objects with this class constructor and generates a sequence of random integers and doubles. The example illustrates that the same sequence is generated when the Random object is created again with the same seed parameter.

' Example of the Random class constructors and Random.NextDouble( )  
' method. 
Imports System.Threading

Module RandomObjectDemo

    ' Generate random numbers from the specified Random object. 
    Sub RunIntNDoubleRandoms( randObj As Random )

        ' Generate the first six random integers. 
        Dim j As Integer 
        For j = 0 To 5
            Console.Write( " {0,10} ", randObj.Next( ) )
        Next j
        Console.WriteLine( )

        ' Generate the first six random doubles. 
        For j = 0 To 5
            Console.Write( " {0:F8} ", randObj.NextDouble( ) )
        Next j
        Console.WriteLine( )
    End Sub  

    ' Create a Random object with the specified seed. 
    Sub FixedSeedRandoms( seed As Integer )

        Console.WriteLine( vbCrLf & _
            "Random numbers from a Random object with " & _
            "seed = {0}:", seed )
        Dim fixRand As New Random( seed )

        RunIntNDoubleRandoms( fixRand )
    End Sub  

    ' Create a random object with a timer-generated seed. 
    Sub AutoSeedRandoms( )

        ' Wait to allow the timer to advance.
        Thread.Sleep( 1 )

        Console.WriteLine( vbCrLf & _
            "Random numbers from a Random object " & _ 
            "with an auto-generated seed:" )
        Dim autoRand As New Random( )

        RunIntNDoubleRandoms( autoRand )
    End Sub  

    Sub Main( )
        Console.WriteLine( _
            "This example of the Random class constructors " & _
            "and Random.NextDouble( ) " & vbCrLf & _
            "generates the following output." & vbCrLf )
        Console.WriteLine( "Create Random " & _
            "objects, and then generate and display six " & _
            "integers and " & vbCrLf & "six doubles from each." )

        FixedSeedRandoms( 123 )
        FixedSeedRandoms( 123 )

        FixedSeedRandoms( 456 )
        FixedSeedRandoms( 456 )

        AutoSeedRandoms( )
        AutoSeedRandoms( )
        AutoSeedRandoms( )
    End Sub 
End Module  

' This example of the Random class constructors and Random.NextDouble( ) 
' generates the following output. 
'  
' Create Random objects, and then generate and display six integers and 
' six doubles from each. 
'  
' Random numbers from a Random object with seed = 123: 
'  2114319875  1949518561  1596751841  1742987178  1586516133   103755708 
'  0.01700087  0.14935942  0.19470390  0.63008947  0.90976122  0.49519146 
'  
' Random numbers from a Random object with seed = 123: 
'  2114319875  1949518561  1596751841  1742987178  1586516133   103755708 
'  0.01700087  0.14935942  0.19470390  0.63008947  0.90976122  0.49519146 
'  
' Random numbers from a Random object with seed = 456: 
'  2044805024  1323311594  1087799997  1907260840   179380355   120870348 
'  0.21988117  0.21026556  0.39236514  0.42420498  0.24102703  0.47310170 
'  
' Random numbers from a Random object with seed = 456: 
'  2044805024  1323311594  1087799997  1907260840   179380355   120870348 
'  0.21988117  0.21026556  0.39236514  0.42420498  0.24102703  0.47310170 
'  
' Random numbers from a Random object with an auto-generated seed: 
'  1920831619  1346865774  2006582766  1968819760   332463652   110770792 
'  0.71326689  0.50383335  0.50446082  0.66312569  0.94517193  0.58059287 
'  
' Random numbers from a Random object with an auto-generated seed: 
'   254927927  1205531663  1984850027   110020849  1438111494  1697714106 
'  0.19383387  0.52067738  0.74162783  0.35063667  0.31247720  0.38773733 
'  
' Random numbers from a Random object with an auto-generated seed: 
'   736507882  1064197552  1963117288   398705585   396275689  1137173773 
'  0.67440084  0.53752140  0.97879483  0.03814764  0.67978248  0.19488178

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

March 2012

Replaced the example.

Customer feedback.

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