`String.Equals`

How can you compare 2 strings for equality? With the VB.NET String.Equals Function in its various syntax forms, including the equals operator, you can do this.

We look at examples of string equality testing. We try to understand the concept of String references and the ReferenceEquals function.

This program first creates 2 String variables. Next, we show the instance Equals method, the Shared Equals method, the equals operator, and ReferenceEquals and Compare.

Info The 2 strings a1 and a2 are equal in character contents so all methods evaluate to True except the ReferenceEquals function.

Detail This method doesn't care about the contents of the String, just its memory location.

And In this example, the 2 variables (a1 and a1) point to different memory locations.

Module Module1
    Sub Main()
        Dim a1 As String = "a" + 1.ToString()
        Dim a2 As String = "a" + 1.ToString()

        If a1.Equals(a2) Then
            Console.WriteLine(1)
        End If

        If String.Equals(a1, a2) Then
            Console.WriteLine(2)
        End If

        If a1 = a2 Then
            Console.WriteLine(3)
        End If

        If String.ReferenceEquals(a1, a2) Then
            Console.WriteLine(4)
        End If

        If String.Compare(a1, a2) = 0 Then
            Console.WriteLine(5)
        End If
    End Sub
End Module1
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5

Operator

At first it seems that the equals operator is the simplest and fastest way to compare strings. After all, it is only one character. But let's look at op_Equality in IL Disassembler.

Note We see that the "=" operator compiles to a String.Equals function call. This will be inlined in Release mode by the JIT compiler.

.method public hidebysig specialname static
        bool  op_Equality(string a,
                          string b) cil managed
{
  // Code size       8 (0x8)
  .maxstack  8
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  call       bool System.String::Equals(string,
                                                  string)
  IL_0007:  ret
} // end of method String::op_Equality

Optimization

Are there any good ways to make String.Equals faster? In my experience, trying to rewrite String.Equals with loops yields a slower method.

Tip One of the best optimizations you can make is to change your program to use shorter Strings.

Tip 2 Another optimization requires that you change your program so the differences in the Strings come near the start.

We examined the String.Equals function, and all the different syntax forms with which you can invoke it, in the VB.NET language.