YongGang Meng's Weblog

Today, I saw an article about Equals and ==, something confuses me. http://forums.asp.net/t/1511559.aspx

So I do it myself.

   1:  static void Main(string[] args)

   2:  {

   3:      DoEQ();

   4:      Console.ReadLine();

   5:  }

   6:   

   7:  private static void DoEQ()

   8:  {

   9:      Console.WriteLine("For value datatype:");

  10:      int i = 6;

  11:      int j = 6;

  12:      int h = 8;

  13:      Console.WriteLine("6==6 {0}",i==j);

  14:      Console.WriteLine("6.Equals(6) {0}", i.Equals(j));

  15:      Console.WriteLine("6==8 {0}", i == h);

  16:      Console.WriteLine("6.Equals(8) {0}", i.Equals(h));

  17:   

  18:      Console.WriteLine();

  19:      Console.WriteLine("For reference datatype:");

  20:      StringBuilder iC = new StringBuilder("My");

  21:      StringBuilder jC = new StringBuilder("My");

  22:      StringBuilder hC = new StringBuilder("My Test");

  23:      Console.WriteLine("StringBuilder('My')==StringBuilder('My') {0}", iC == jC);

  24:      Console.WriteLine("StringBuilder('My').Equals(StringBuilder('My')) {0}", iC.Equals(jC));

  25:      Console.WriteLine("StringBuilder('My')==StringBuilder('My Test') {0}", iC == hC);

  26:      Console.WriteLine("StringBuilder('My').Equals(StringBuilder('My Test')) {0}", iC.Equals(hC));

  27:   

  28:      Console.WriteLine();

  29:      Console.WriteLine("For special reference datatype(string):");

  30:      string iStr = "Test";

  31:      string jStr = "Test";

  32:      string hStr = "Just a Test";

  33:      Console.WriteLine("\"Test\"==\"Test\" {0}", iStr == jStr);

  34:      Console.WriteLine("\"Test\".Equals(\"Test\") {0}", iStr.Equals(jStr));

  35:      Console.WriteLine("\"Test\"==\"Just a Test\" {0}", iStr == hStr);

  36:      Console.WriteLine("\"Test\".Equals(\"Just a Test\") {0}", iStr.Equals(hStr));

  37:   

  38:      Console.WriteLine();

  39:      Console.WriteLine("For null and  reference datatype:");

  40:      string iN = null;

  41:      string jN = null;

  42:      string hN = "Test";

  43:      Console.WriteLine("Null==Null {0}", iN == jN);

  44:      //Console.WriteLine("Null.Equals(Null) {0}", iN.Equals(jN));

  45:      Console.WriteLine("Null==\"Test\" {0}", iN == hN);

  46:      //Console.WriteLine("Null.Equals(\"Test\") {0}", iN.Equals(hN));

  47:      Console.WriteLine("\"Test\".Equals(Null) {0}", hN.Equals(iN));

  48:   

  49:      Console.WriteLine();

  50:      Console.WriteLine("For special value datatype(zero):");

  51:      int iZ = 0;

  52:      short jZ =0;

  53:      Console.WriteLine("0i==0s {0}", iZ == jZ);

  54:      Console.WriteLine("0i.Equals(0s) {0}", iZ.Equals(jZ));

  55:  }

   1:  [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]

   2:  public virtual bool Equals(object obj)

   3:  {

   4:      return RuntimeHelpers.Equals(this, obj);

   5:  }

   1:  [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]

   2:  public static bool Equals(object objA, object objB)

   3:  {

   4:      return ((objA == objB) || (((objA != null) && (objB != null)) && objA.Equals(objB)));

   5:  }

   1:  [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success), TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]

   2:  public static bool ReferenceEquals(object objA, object objB)

   3:  {

   4:      return (objA == objB);

   5:  }