Reference types

Question

 var a = MyClassInstance;
    MyClassInstance = null;
    //if (a !=null){ //why }

I think that a points to MyClassInstance and MyClassInstance equals null, then a must be equals null too. But a is not null and I don't understand why.

Answer 1

a and MyClassInstance are references to an object.
Changing one reference doesn't change the other.

var a = MyClassInstance; // Both references point to the same object
MyClassInstance = null;  // MyClassInstance now points to null, a is not affected

Answer 2

The variable a is a reference, so the value it holds is the "location" of some object. MyClassInstance is also a reference. By setting a = MyClassInstance they both point to the same instance. Setting MyClassInstance to null affects that reference only. It doesn't affect the object itself and it doesn't affect any other references.