Random Constructors
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Initializes a new instance of the Random class.
Random() |
Initializes a new instance of the Random class using a default seed value. |
Random(Int32) |
Initializes a new instance of the Random class, using the specified seed value. |
- Source:
- Random.cs
- Source:
- Random.cs
- Source:
- Random.cs
Initializes a new instance of the Random class using a default seed value.
public:
Random();
public Random ();
Public Sub New ()
Examples
The following example uses the parameterless constructor to instantiate three Random objects and displays a sequence of five random integers for each. If it is run on .NET Framework, because the first two Random objects are created in close succession, they are instantiated using identical seed values based on the system clock and, therefore, they produce an identical sequence of random numbers. On the other hand, the parameterless constructor of the third Random object is called after a two-second delay caused by calling the Thread.Sleep method. Because this produces a different seed value for the third Random object, it produces a different sequence of random numbers.
using System;
using System.Threading;
public class RandomNumbers
{
public static void Main()
{
Random rand1 = new Random();
Random rand2 = new Random();
Thread.Sleep(2000);
Random rand3 = new Random();
ShowRandomNumbers(rand1);
ShowRandomNumbers(rand2);
ShowRandomNumbers(rand3);
}
private static void ShowRandomNumbers(Random rand)
{
Console.WriteLine();
byte[] values = new byte[5];
rand.NextBytes(values);
foreach (byte value in values)
Console.Write("{0, 5}", value);
Console.WriteLine();
}
}
// The example displays an output similar to the following:
// 28 35 133 224 58
//
// 28 35 133 224 58
//
// 32 222 43 251 49
open System
open System.Threading
let showRandomNumbers (rand: Random) =
printfn ""
let values = Array.zeroCreate 5
rand.NextBytes values
for value in values do
printf "%5i" value
printfn ""
let rand1 = Random()
let rand2 = Random()
Thread.Sleep 2000
let rand3 = Random()
showRandomNumbers rand1
showRandomNumbers rand2
showRandomNumbers rand3
// The example displays an output similar to the following:
// 28 35 133 224 58
//
// 28 35 133 224 58
//
// 32 222 43 251 49
Imports System.Threading
Module RandomNumbers
Public Sub Main()
Dim rand1 As New Random()
Dim rand2 As New Random()
Thread.Sleep(2000)
Dim rand3 As New Random()
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 an output similar to the following:
' 28 35 133 224 58
'
' 28 35 133 224 58
'
' 32 222 43 251 49
Remarks
In .NET Framework, the default seed value is derived from the system clock, which has finite resolution. As a result, different Random objects that are created in close succession by a call to the parameterless constructor have identical default seed values and, therefore, produce identical sets of random numbers. You can avoid this problem by using a single Random object to generate all random numbers. You can also work around it by generating your own random seed value and passing it to the Random(Int32) constructor. For more information, see the Random(Int32) constructor.
In .NET Core, the default seed value is produced by the thread-static, pseudo-random number generator, so the previously described limitation does not apply. Different Random objects created in close succession produce different sets of random numbers in .NET Core.
Call this constructor if you want your random number generator to generate a random sequence of numbers. To generate a fixed sequence of random numbers that will be the same for different random number generators, call the Random(Int32) constructor with a fixed seed value. This Random constructor overload is frequently used when testing apps that use random numbers.
Once you've instantiated the random number generator, you call individual Random methods, such as Next() or NextDouble(), to generate random numbers.
Applies to
.NET 9 及其他版本
產品 | 版本 |
---|---|
.NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1 |
UWP | 10.0 |
- Source:
- Random.cs
- Source:
- Random.cs
- Source:
- Random.cs
Initializes a new instance of the Random class, using the specified seed value.
public:
Random(int Seed);
public Random (int Seed);
new Random : int -> Random
Public Sub New (Seed As Integer)
Parameters
- Seed
- 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.
Examples
The following example creates Random objects with the class constructor that takes a seed parameter 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 constructor and seed parameter.
// Example of the Random class constructors and Random::NextDouble()
// method.
using namespace System;
using namespace System::Threading;
// Generate random numbers from the specified Random object.
void RunIntNDoubleRandoms(Random^ randObj)
{
// Generate the first six random integers.
for (int j = 0; j < 6; j++)
Console::Write(" {0,10} ", randObj->Next());
Console::WriteLine();
// Generate the first six random doubles.
for (int j = 0; j < 6; j++)
Console::Write(" {0:F8} ", randObj->NextDouble());
Console::WriteLine();
}
// Create a Random object with the specified seed.
void FixedSeedRandoms(int seed)
{
Console::WriteLine("\nRandom numbers from a Random object with seed = {0}:", seed);
Random^ fixRand = gcnew Random(seed);
RunIntNDoubleRandoms(fixRand);
}
// Create a random object with a timer-generated seed.
void AutoSeedRandoms()
{
// Wait to allow the timer to advance.
Thread::Sleep(1);
Console::WriteLine("\nRandom numbers from a Random object "
"with an auto-generated seed:");
Random^ autoRand = gcnew Random;
RunIntNDoubleRandoms(autoRand);
}
int main()
{
Console::WriteLine("This example of the Random class constructors and Random"
"::NextDouble() \ngenerates the following output.\n");
Console::WriteLine("Create Random objects, and then generate and "
"display six integers and \nsix doubles from each.");
FixedSeedRandoms(123);
FixedSeedRandoms(123);
FixedSeedRandoms(456);
FixedSeedRandoms(456);
AutoSeedRandoms();
AutoSeedRandoms();
AutoSeedRandoms();
}
/*
This example of the Random class constructors and Random::NextDouble()
generates an output similar to the following:
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:
1624372556 1894939458 302472229 588108304 23919954 1085111949
0.14595512 0.30162298 0.92267372 0.55707657 0.25430079 0.74143239
Random numbers from a Random object with an auto-generated seed:
2105952511 1753605347 280739490 876793040 1129567796 524571616
0.62652210 0.31846701 0.15984073 0.24458755 0.62160607 0.54857684
Random numbers from a Random object with an auto-generated seed:
440048819 1612271236 259006751 1165477776 87731991 2111514930
0.10708907 0.33531104 0.39700773 0.93209853 0.98891135 0.35572129
*/
// Example of the Random class constructors and Random.NextDouble()
// method.
using System;
using System.Threading;
public class RandomObjectDemo
{
// Generate random numbers from the specified Random object.
static void RunIntNDoubleRandoms(Random randObj)
{
// Generate the first six random integers.
for(int j = 0; j < 6; j++)
Console.Write(" {0,10} ", randObj.Next());
Console.WriteLine();
// Generate the first six random doubles.
for(int j = 0; j < 6; j++)
Console.Write(" {0:F8} ", randObj.NextDouble());
Console.WriteLine();
}
// Create a Random object with the specified seed.
static void FixedSeedRandoms(int seed)
{
Console.WriteLine(
"\nRandom numbers from a Random object with " +
"seed = {0}:", seed);
Random fixRand = new Random(seed);
RunIntNDoubleRandoms(fixRand);
}
// Create a random object with a timer-generated seed.
static void AutoSeedRandoms()
{
// Wait to allow the timer to advance.
Thread.Sleep(1);
Console.WriteLine(
"\nRandom numbers from a Random object " +
"with an auto-generated seed:");
Random autoRand = new Random();
RunIntNDoubleRandoms(autoRand);
}
static void Main()
{
Console.WriteLine(
"This example of the Random class constructors and " +
"Random.NextDouble() \n" +
"generates the following output.\n");
Console.WriteLine(
"Create Random objects, and then generate and " +
"display six integers and \nsix doubles from each.");
FixedSeedRandoms(123);
FixedSeedRandoms(123);
FixedSeedRandoms(456);
FixedSeedRandoms(456);
AutoSeedRandoms();
AutoSeedRandoms();
AutoSeedRandoms();
}
}
/*
This example of the Random class constructors and Random.NextDouble()
generates an output similar to the following:
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:
380213349 127379247 1969091178 1983029819 1963098450 1648433124
0.08824121 0.41249688 0.36445811 0.05637512 0.62702451 0.49595560
Random numbers from a Random object with an auto-generated seed:
861793304 2133528783 1947358439 124230908 921262645 1087892791
0.56880819 0.42934091 0.60162512 0.74388610 0.99432979 0.30310005
Random numbers from a Random object with an auto-generated seed:
1343373259 1992194672 1925625700 412915644 2026910487 527352458
0.04937517 0.44618494 0.83879212 0.43139707 0.36163507 0.11024451
*/
// Example of the Random class constructors and Random.NextDouble()
// method.
open System
open System.Threading
// Generate random numbers from the specified Random object.
let runIntNDoubleRandoms (randObj: Random) =
// Generate the first six random integers.
for _ = 1 to 6 do
printf $" {randObj.Next(),10} "
printfn ""
// Generate the first six random doubles.
for _ = 1 to 6 do
printf $" {randObj.NextDouble():F8} "
printfn ""
let fixedSeedRandoms seed =
printfn $"\nRandom numbers from a Random object with seed = %i{seed}:"
let fixRand = Random seed
runIntNDoubleRandoms fixRand
let autoSeedRandoms () =
// Wait to allow the timer to advance.
Thread.Sleep 1
printfn "\nRandom numbers from a Random object with an auto-generated seed: "
let autoRand = Random ()
runIntNDoubleRandoms autoRand
printfn
"""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."""
fixedSeedRandoms 123
fixedSeedRandoms 123
fixedSeedRandoms 456
fixedSeedRandoms 456
autoSeedRandoms ()
autoSeedRandoms ()
autoSeedRandoms ()
(*
This example of the Random class constructors and Random.NextDouble()
generates an output similar to the following:
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:
380213349 127379247 1969091178 1983029819 1963098450 1648433124
0.08824121 0.41249688 0.36445811 0.05637512 0.62702451 0.49595560
Random numbers from a Random object with an auto-generated seed:
861793304 2133528783 1947358439 124230908 921262645 1087892791
0.56880819 0.42934091 0.60162512 0.74388610 0.99432979 0.30310005
Random numbers from a Random object with an auto-generated seed:
1343373259 1992194672 1925625700 412915644 2026910487 527352458
0.04937517 0.44618494 0.83879212 0.43139707 0.36163507 0.11024451
*)
' 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 an output similar to the following:
'
' 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
Remarks
Providing an identical seed value to different Random objects causes each instance to produce identical sequences of random numbers. This is often done when testing apps that rely on random number generators.
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, as the Random() overload does. However, the system clock might not have sufficient resolution to provide different invocations of this constructor with a different seed value. On the .NET Framework, 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.
using System;
using System.Threading;
public class Example
{
public static void Main()
{
Random rand1 = new Random((int) DateTime.Now.Ticks & 0x0000FFFF);
Random rand2 = new Random((int) DateTime.Now.Ticks & 0x0000FFFF);
Thread.Sleep(20);
Random rand3 = new Random((int) DateTime.Now.Ticks & 0x0000FFFF);
ShowRandomNumbers(rand1);
ShowRandomNumbers(rand2);
ShowRandomNumbers(rand3);
}
private static void ShowRandomNumbers(Random rand)
{
Console.WriteLine();
byte[] values = new byte[4];
rand.NextBytes(values);
foreach (var value in values)
Console.Write("{0, 5}", value);
Console.WriteLine();
}
}
// The example displays output similar to the following:
// 145 214 177 134 173
//
// 145 214 177 134 173
//
// 126 185 175 249 157
open System
open System.Threading
let showRandomNumbers (rand: Random) =
printfn ""
let values = Array.zeroCreate 5
rand.NextBytes values
for value in values do
printf "%5i" value
printfn ""
let rand1 = Random(DateTime.Now.Ticks &&& 0x0000FFFFL |> int)
let rand2 = Random(DateTime.Now.Ticks &&& 0x0000FFFFL |> int)
Thread.Sleep 20
let rand3 = Random(DateTime.Now.Ticks &&& 0x0000FFFFL |> int)
showRandomNumbers rand1
showRandomNumbers rand2
showRandomNumbers rand3
// The example displays output similar to the following:
// 145 214 177 134 173
//
// 145 214 177 134 173
//
// 126 185 175 249 157
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
Another option is to instantiate a single Random object that you use to generate all the random numbers in your application. This yields slightly better performance, since instantiating a random number generator is fairly expensive.
Applies to
.NET 9 及其他版本
產品 | 版本 |
---|---|
.NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1 |
UWP | 10.0 |