Why would you use String Equals over

Question

I recently was introduced to a large codebase and noticed all string comparisons are done using String Equals   instead of      What s the reason for this  do you think

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It s entirely likely that a large portion of the developer base comes from a Java background where using    to compare strings is wrong and doesn t work   In C  there s no  practical  difference  for strings  as long as they are typed as string   If they are typed as object or T then see other answers here that talk about generic methods or operator overloading as there you definitely want to use the Equals method

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There s a writeup on this article which you might find to be interesting  with some quotes from Jon Skeet  It seems like the use is pretty much the same      Jon Skeet states that the performance of instance Equals  is slightly better when the strings are short   as the strings increase in length  that difference becomes completely insignificant

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Both methods do the same functionally - they compare values  As is written on MSDN    About String Equals method - Determines whether this instance and another specified String object have the same value   http   msdn microsoft com en-us library 858x0yyx aspx  About    - Although string is a reference type  the equality operators     and     are defined to compare the values of string objects  not references  This makes testing for string equality more intuitive   http   msdn microsoft com en-en library 362314fe aspx    But if one of your string instances is null  these methods are working differently   string x   null  string y    qq   if  x    y     returns false     MessageBox Show  true    else     MessageBox Show  false     if  x Equals y      returns System NullReferenceException  Object reference not set to an instance of an object  - because x is null         MessageBox Show  true    else     MessageBox Show  false

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There is practical difference between string Equals and     bool result   false   object obj    String       string str2    String   string str3   typeof string  Name  string str4    String   object obj2   str3      Comparision between object obj and string str2 -- Com 1 result   string Equals obj  str2     true result   String ReferenceEquals obj  str2      true result    obj    str2     true     Comparision between object obj and string str3 -- Com 2 result   string Equals obj  str3     true result   String ReferenceEquals obj  str3      false result    obj    str3     false     Comparision between object obj and string str4 -- Com 3 result   string Equals obj  str4     true result   String ReferenceEquals obj  str4      true result    obj    str4     true     Comparision between string str2 and string str3 -- Com 4 result   string Equals str2  str3     true result   String ReferenceEquals str2  str3      false result    str2    str3     true     Comparision between string str2 and string str4 -- Com 5 result   string Equals str2  str4     true result   String ReferenceEquals str2  str4      true result    str2    str4     true     Comparision between string str3 and string str4 -- Com 6 result   string Equals str3  str4     true result   String ReferenceEquals str3  str4      false result    str3    str4     true     Comparision between object obj and object obj2 -- Com 7 result   String Equals obj  obj2     true result   String ReferenceEquals obj  obj2      false result    obj    obj2     false   Adding Watch  obj      String   1     object  string  str2     String   1     string str3     String   5     string str4     String   1     string obj2     String   5     object  string    Now look at  1   and  5    obj  str2  str4 and obj2 references are same    obj and obj2 are object type and others are string type  Conclusion    com1  result    obj    str2     true   compares object and string so performs a reference equality check obj and str2 point to the same reference so the result is true  com2  result    obj    str3     false   compares object and string so performs a reference equality check obj and str3 point to the different references so the result is false  com3  result    obj    str4     true   compares object and string so performs a reference equality check obj and str4 point to the same reference so the result is true  com4  result    str2    str3     true   compares string and string so performs a string value check str2 and str3 are both  String  so the result is true  com5  result    str2    str4     true   compares string and string so performs a string value check str2 and str4 are both  String  so the result is true  com6  result    str3    str4     true   compares string and string so performs a string value check str3 and str4 are both  String  so the result is true  com7  result    obj    obj2     false   - compares object and object so performs a reference equality check         - obj and obj2 point to the different references so the result is false

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There is one subtle but very important difference between    and the String Equals methods   class Program       static void Main string   args                CheckEquality  a    a            Console WriteLine  ----------            CheckEquality  a    ba  Substring 1               static void CheckEquality lt T gt  T value1  T value2  where T   class               Console WriteLine  value1   0    value1           Console WriteLine  value2   0    value2            Console WriteLine  value1    value2        0    value1    value2           Console WriteLine  value1 Equals value2    0    value1 Equals value2             if  typeof T  IsEquivalentTo typeof string                          string string1    string  object value1              string string2    string  object value2              Console WriteLine  string1    string2      0    string1    string2                       Produces this output    value1  a value2  a value1    value2       True value1 Equals value2   True string1    string2     True ---------- value1  a value2  a value1    value2       False value1 Equals value2   True string1    string2     True    You can see that the    operator is returning false to two obviously equal strings  Why  Because the    operator in use in the generic method is resolved to be the op equal method as defined by System Object  the only guarantee of T the method has at compile time   which means that it s reference equality instead of value equality   When you have two values typed as System String explicitly  then    has a value-equality semantic because the compiler resolves the    to System String op equal instead of System Object op equal   So to play it safe  I almost always use String Equals instead to that I always get the value equality semantics I want   And to avoid NullReferenceExceptions if one of the values is null  I always use the static String Equals method   bool true   String Equals  a    ba  Substring 1

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String Equals does offer overloads to handle casing and culture-aware comparison   If your code doesn t make use of these  the devs may just be used to Java  where  as Matthew says   you must use the  Equals method to do content comparisons

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I ve just been banging my head against a wall trying to solve a bug because I read this page and concluded there was no meaningful difference when in practice there is so I ll post this link here in case anyone else finds they get different results out of    and equals   Object    equality fails  but  Equals succeeds  Does this make sense   string a    x   string b   new String new     x      Console WriteLine  x    x      a    b     True Console WriteLine  object x    x       object a     object b     False Console WriteLine  x equals x      a Equals b      True Console WriteLine  object x equals x        object a  Equals  object b      True

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I want to add that there is another difference  It is related to what Andrew posts   It is also related to a VERY annoying to find bug in our software  See the following simplified example  I also omitted the null check    public const int SPECIAL NUMBER   213   public bool IsSpecialNumberEntered string numberTextBoxTextValue        return numberTextBoxTextValue Equals SPECIAL NUMBER      This will compile and always return false  While the following will give a compile error   public const int SPECIAL NUMBER   213   public bool IsSpecialNumberEntered string numberTextBoxTextValue        return  numberTextBoxTextValue    SPECIAL NUMBER       We have had to solve a similar problem where someone compared enums of different type using Equals  You are going to read over this MANY times before realising it is the cause of the bug  Especially if the definition of SPECIAL NUMBER is not near the problem area   This is why I am really against the use of Equals in situations where is it not necessary  You lose a little bit of type-safety

[c#] Why would you use String.Equals over ==?

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