Represents a pseudo-random number generator, a device that produces a sequence of numbers that meet certain statistical requirements for randomness.
(in mscorlib.dll)
Visual Basic (Declaration)
<ComVisibleAttribute(True)> _
Public Class Random
[ComVisibleAttribute(true)]
public class Random
Pseudo-random numbers are chosen with equal probability from a finite set of numbers. The chosen numbers are not completely random because a definite mathematical algorithm is used to select them, but they are sufficiently random for practical purposes. The current implementation of the Random class is based on Donald E. Knuth's subtractive random number generator algorithm. For more information, see D. E. Knuth. "The Art of Computer Programming, volume 2: Seminumerical Algorithms". Addison-Wesley, Reading, MA, second edition, 1981.
The random number generation starts from a seed value. If the same seed is used repeatedly, the same series of numbers is generated. One way to produce different sequences is to make the seed value time-dependent, thereby producing a different series with each new instance of Random. By default, the parameterless constructor of the Random class uses the system clock to generate its seed value, while its parameterized constructor can take an Int32 value based on the number of ticks in the current time. However, because the clock has finite resolution, using the parameterless constructor to create different Random objects in close succession creates random number generators that produce identical sequences of random numbers. The following example illustrates that two Random objects that are instantiated in close sucession generate an identical series of random numbers.
Dim bytes1(99), bytes2(99) As Byte
Dim rnd1 As New Random()
Dim rnd2 As New Random()
rnd1.NextBytes(bytes1)
rnd2.NextBytes(bytes2)
outputBlock.Text += "First Series:" & vbCrLf
For ctr As Integer = bytes1.GetLowerBound(0) To bytes1.GetUpperBound(0)
outputBlock.Text += String.Format("{0, 5}", bytes1(ctr))
If (ctr + 1) Mod 10 = 0 Then outputBlock.Text &= vbCrLf
Next
outputBlock.Text += vbCrLf
outputBlock.Text += "Second Series:" & vbCrLf
For ctr As Integer = bytes2.GetLowerBound(0) To bytes2.GetUpperBound(0)
outputBlock.Text += String.Format("{0, 5}", bytes2(ctr))
If (ctr + 1) Mod 10 = 0 Then outputBlock.Text &= vbCrLf
Next
' The example displays the following output:
' First Series:
' 97 129 149 54 22 208 120 105 68 177
' 113 214 30 172 74 218 116 230 89 18
' 12 112 130 105 116 180 190 200 187 120
' 7 198 233 158 58 51 50 170 98 23
' 21 1 113 74 146 245 34 255 96 24
' 232 255 23 9 167 240 255 44 194 98
' 18 175 173 204 169 171 236 127 114 23
' 167 202 132 65 253 11 254 56 214 127
' 145 191 104 163 143 7 174 224 247 73
' 52 6 231 255 5 101 83 165 160 231
'
' Second Series:
' 97 129 149 54 22 208 120 105 68 177
' 113 214 30 172 74 218 116 230 89 18
' 12 112 130 105 116 180 190 200 187 120
' 7 198 233 158 58 51 50 170 98 23
' 21 1 113 74 146 245 34 255 96 24
' 232 255 23 9 167 240 255 44 194 98
' 18 175 173 204 169 171 236 127 114 23
' 167 202 132 65 253 11 254 56 214 127
' 145 191 104 163 143 7 174 224 247 73
' 52 6 231 255 5 101 83 165 160 231
byte[] bytes1 = new byte[100];
byte[] bytes2 = new byte[100];
Random rnd1 = new Random();
Random rnd2 = new Random();
rnd1.NextBytes(bytes1);
rnd2.NextBytes(bytes2);
outputBlock.Text += "First Series:" + "\n";
for (int ctr = bytes1.GetLowerBound(0);
ctr <= bytes1.GetUpperBound(0);
ctr++)
{
outputBlock.Text += String.Format("{0, 5}", bytes1[ctr]);
if ((ctr + 1) % 10 == 0) outputBlock.Text += "\n";
}
outputBlock.Text += "\n";
outputBlock.Text += "Second Series:" + "\n";
for (int ctr = bytes2.GetLowerBound(0);
ctr <= bytes2.GetUpperBound(0);
ctr++)
{
outputBlock.Text += String.Format("{0, 5}", bytes2[ctr]);
if ((ctr + 1) % 10 == 0) outputBlock.Text += "\n";
}
// The example displays the following output:
// First Series:
// 97 129 149 54 22 208 120 105 68 177
// 113 214 30 172 74 218 116 230 89 18
// 12 112 130 105 116 180 190 200 187 120
// 7 198 233 158 58 51 50 170 98 23
// 21 1 113 74 146 245 34 255 96 24
// 232 255 23 9 167 240 255 44 194 98
// 18 175 173 204 169 171 236 127 114 23
// 167 202 132 65 253 11 254 56 214 127
// 145 191 104 163 143 7 174 224 247 73
// 52 6 231 255 5 101 83 165 160 231
//
// Second Series:
// 97 129 149 54 22 208 120 105 68 177
// 113 214 30 172 74 218 116 230 89 18
// 12 112 130 105 116 180 190 200 187 120
// 7 198 233 158 58 51 50 170 98 23
// 21 1 113 74 146 245 34 255 96 24
// 232 255 23 9 167 240 255 44 194 98
// 18 175 173 204 169 171 236 127 114 23
// 167 202 132 65 253 11 254 56 214 127
// 145 191 104 163 143 7 174 224 247 73
// 52 6 231 255 5 101 83 165 160 231
This problem can be avoided by creating a single Random object rather than multiple ones.
To improve performance, create one Random object to generate many random numbers over time, instead of repeatedly creating new Random objects to generate one random number.
To generate a cryptographically secure random number suitable for creating a random password, for example, use a class derived from System.Security.Cryptography..::.RandomNumberGenerator such as System.Security.Cryptography..::.RNGCryptoServiceProvider.
Notes to Inheritors: The Random..::.Next()()(), Random..::.Next(Int32, Int32), and NextBytes methods do not necessarily call the derived class implementation of the Sample method. As a result, classes derived from Random should override all three of these methods.
The following example creates a single random number generator and calls its NextBytes, Next, and NextDouble methods to generate sequences of random numbers within different ranges.
' Instantiate random number generator using system-supplied value as seed.
Dim rand As New Random()
' Generate and display 5 random byte (integer) values.
Dim bytes(4) As Byte
rand.NextBytes(bytes)
outputBlock.Text += "Five random byte values:" & vbCrLf
For Each byteValue As Byte In bytes
outputBlock.Text += String.Format("{0, 5}", byteValue)
Next
outputBlock.Text += vbCrLf
' Generate and display 5 random integers.
outputBlock.Text += "Five random integer values:" & vbCrLf
For ctr As Integer = 0 To 4
outputBlock.Text += String.Format("{0,15:N0}", rand.Next)
Next
outputBlock.Text += vbCrLf
' Generate and display 5 random integers between 0 and 100.'
outputBlock.Text += "Five random integers between 0 and 100:" & vbCrLf
For ctr As Integer = 0 To 4
outputBlock.Text += String.Format("{0,8:N0}", rand.Next(101))
Next
outputBlock.Text += vbCrLf
' Generate and display 5 random integers from 50 to 100.
outputBlock.Text += "Five random integers between 50 and 100:" & vbCrLf
For ctr As Integer = 0 To 4
outputBlock.Text += String.Format("{0,8:N0}", rand.Next(50, 101))
Next
outputBlock.Text += vbCrLf
' Generate and display 5 random floating point values from 0 to 1.
outputBlock.Text += "Five Doubles." & vbCrLf
For ctr As Integer = 0 To 4
outputBlock.Text += String.Format("{0,8:N3}", rand.NextDouble())
Next
outputBlock.Text += vbCrLf
' Generate and display 5 random floating point values from 0 to 5.
outputBlock.Text += "Five Doubles between 0 and 5." & vbCrLf
For ctr As Integer = 0 To 4
outputBlock.Text += String.Format("{0,8:N3}", rand.NextDouble() * 5)
Next
' Sample console output might appear as follows:
' Five random byte values:
' 194 185 239 54 116
' Five random integer values:
' 507,353,531 1,509,532,693 2,125,074,958 1,409,512,757 652,767,128
' Five random integers between 0 and 100:
' 16 78 94 79 52
' Five random integers between 50 and 100:
' 56 66 96 60 65
' Five Doubles.
' 0.943 0.108 0.744 0.563 0.415
' Five Doubles between 0 and 5.
' 2.934 3.130 0.292 1.432 4.369
// Instantiate random number generator using system-supplied value as seed.
Random rand = new Random();
// Generate and display 5 random byte (integer) values.
byte[] bytes = new byte[4];
rand.NextBytes(bytes);
outputBlock.Text += "Five random byte values:" + "\n";
foreach (byte byteValue in bytes)
outputBlock.Text += String.Format("{0, 5}", byteValue);
outputBlock.Text += "\n";
// Generate and display 5 random integers.
outputBlock.Text += "Five random integer values:" + "\n";
for (int ctr = 0; ctr <= 4; ctr++)
outputBlock.Text += String.Format("{0,15:N0}", rand.Next());
outputBlock.Text += "\n";
// Generate and display 5 random integers between 0 and 100.//
outputBlock.Text += "Five random integers between 0 and 100:" + "\n";
for (int ctr = 0; ctr <= 4; ctr++)
outputBlock.Text += String.Format("{0,8:N0}", rand.Next(101));
outputBlock.Text += "\n";
// Generate and display 5 random integers from 50 to 100.
outputBlock.Text += "Five random integers between 50 and 100:" + "\n";
for (int ctr = 0; ctr <= 4; ctr++)
outputBlock.Text += String.Format("{0,8:N0}", rand.Next(50, 101));
outputBlock.Text += "\n";
// Generate and display 5 random floating point values from 0 to 1.
outputBlock.Text += "Five Doubles." + "\n";
for (int ctr = 0; ctr <= 4; ctr++)
outputBlock.Text += String.Format("{0,8:N3}", rand.NextDouble());
outputBlock.Text += "\n";
// Generate and display 5 random floating point values from 0 to 5.
outputBlock.Text += "Five Doubles between 0 and 5." + "\n";
for (int ctr = 0; ctr <= 4; ctr++)
outputBlock.Text += String.Format("{0,8:N3}", rand.NextDouble() * 5);
// Sample console output might appear as follows:
// Five random byte values:
// 194 185 239 54 116
// Five random integer values:
// 507,353,531 1,509,532,693 2,125,074,958 1,409,512,757 652,767,128
// Five random integers between 0 and 100:
// 16 78 94 79 52
// Five random integers between 50 and 100:
// 56 66 96 60 65
// Five Doubles.
// 0.943 0.108 0.744 0.563 0.415
// Five Doubles between 0 and 5.
// 2.934 3.130 0.292 1.432 4.369
System..::.Object
System..::.Random
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
Reference