c# - Are string.Equals() and == operator really same?

Question

This question already has answers here:

Answer 1

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