Are string.Equals() and == operator really same? [duplicate]

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Two differences:

  • Equals is polymorphic (i.e. it can be overridden, and the implementation used will depend on the execution-time type of the target object), whereas the implementation of == used is determined based on the compile-time types of the objects:

      // Avoid getting confused by interning
  object x = new StringBuilder("hello").ToString();
  object y = new StringBuilder("hello").ToString();
  if (x.Equals(y)) // Yes

  // The compiler doesn't know to call ==(string, string) so it generates
  // a reference comparision instead
  if (x == y) // No

  string xs = (string) x;
  string ys = (string) y;

  // Now *this* will call ==(string, string), comparing values appropriately
  if (xs == ys) // Yes

  • Equals will throw an exception if you call it on null, == won’t

      string x = null;
  string y = null;

  if (x.Equals(y)) // NullReferenceException

  if (x == y) // Yes

Note that you can avoid the latter being a problem using object.Equals:

if (object.Equals(x, y)) // Fine even if x or y is null

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