Article
11/17/2011

String.Join Method (String, array<Object[])

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Concatenates the elements of an object array, using the specified separator between each element.

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

Syntax

'Declaration
<ComVisibleAttribute(False)> _
Public Shared Function Join ( _
    separator As String, _
    ParamArray values As Object() _
) As String

[ComVisibleAttribute(false)]
public static string Join(
    string separator,
    params Object[] values
)

Parameters

separator
Type: System.String
The string to use as a separator.

values
Type: array<System.Object[]
An array that contains the elements to concatenate.

Return Value

Type: System.String
A string that consists of the elements of values delimited by the separator string. If values is an empty array, the method returns String.Empty.

Exceptions

Exception	Condition
ArgumentNullException	values is nulla null reference (Nothing in Visual Basic).

Remarks

If separator is nulla null reference (Nothing in Visual Basic), an empty string (String.Empty) is used instead. If any element of values other than the first element is null, an empty string (String.Empty) is used instead.

Join(String, array<Object[]) is a convenience method that lets you concatenate each element in an object array without explicitly converting its elements to strings. The string representation of each object in the array is derived by calling that object's ToString method.

Notes to Callers

If the first element of values is nulla null reference (Nothing in Visual Basic), the Join method does not concatenate the elements in values but instead returns String.Empty. A number of workarounds for this issue are available. The easiest is to assign a value of String.Empty to the first element of the array, as the following example shows.

Dim values() As Object = {Nothing, "Cobb", 4189, 11434, 0.366}
If values(0) Is Nothing Then values(0) = String.Empty
outputBlock.Text += String.Join("|", values) & vbCrLf
' The example displays the following output:
'      |Cobb|4189|11434|0.366

object[] values = { null, "Cobb", 4189, 11434, .366 };
if (values[0] == null) values[0] = String.Empty;
outputBlock.Text += String.Join("|", values) + "\n";
// The example displays the following output:
//      |Cobb|4189|11434|0.366

Examples

The following example uses the Sieve of Eratosthenes algorithm to calculate the prime numbers that are less than or equal to 100. It assigns the result to a integer array, which it then passes to the Join(String, array<Object[]) method.

Imports System.Collections.Generic

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim maxPrime As Integer = 100
      Dim primes() As Integer = GetPrimes(maxPrime)
      outputBlock.Text += String.Format("Primes less than {0}:", maxPrime) & vbCrLf
      outputBlock.Text += String.Format("   {0}", String.Join(" ", primes)) & vbCrLf
   End Sub

   Private Function GetPrimes(ByVal maxPrime As Integer) As Integer()
      Dim values(maxPrime) As Integer
      ' Use Sieve of Erathsthenes to determine prime numbers.
      For ctr As Integer = 2 To _
                           CInt(Math.Ceiling(Math.Sqrt(values.GetUpperBound(0))))
         If values(ctr) = 1 Then Continue For

         For multiplier As Integer = ctr To maxPrime \ 2
            If ctr * multiplier <= maxPrime Then values(ctr * multiplier) = 1
         Next
      Next

      Dim primes As New List(Of Integer)
      For ctr As Integer = 2 To values.GetUpperBound(0)
         If values(ctr) = 0 Then primes.Add(ctr)
      Next
      Return primes.ToArray()
   End Function
End Module
' The example displays the following output:
'    Primes less than 100:
'       2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

using System;
using System.Collections.Generic;

public class Example
{ 
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      int maxPrime = 100;
      int[] primes = GetPrimes(maxPrime);
      outputBlock.Text += String.Format("Primes less than {0}:", maxPrime) + "\n";
      outputBlock.Text += String.Format("   {0}", String.Join(" ", primes)) + "\n";
   }

   private static int[] GetPrimes(int maxPrime)
   {  
      int[] values = new int[maxPrime + 1];
      // Use Sieve of Erathsthenes to determine prime numbers.

      for (int ctr = 2; ctr <= (int)Math.Ceiling(Math.Sqrt(values.GetUpperBound(0))); ctr++)
      {
         if (values[ctr] == 1) continue;

         for (int multiplier = ctr; multiplier <= maxPrime / 2; multiplier++)
            if (ctr * multiplier < maxPrime + 1)
               values[ctr * multiplier] = 1;
      }

      List<int> primes = new List<int>();
      for (int ctr = 2; ctr <= values.GetUpperBound(0); ctr++)
         if (values[ctr] == 0)
            primes.Add(ctr);

      return primes.ToArray();
   }
}
// The example displays the following output:
//    Primes less than 100:
//       2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Version Information

Silverlight

Supported in: 5, 4

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Change History

Date	History	Reason
	Clarified the effect of elements with null values in the Remarks section.	Content bug fix.
January 2011	Added the Notes for Callers section.	Content bug fix.

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