The java.lang.Class.isInstance() determines if the specified Object is assignment-compatible with the object represented by this Class
Java’s isInstance() method’s equivalent in C# is IsAssignableFrom().
Another simplest way for isInstance() equivalent is −
bool res = (ob is DemoClass);
You can also work with Type.IsInstanceOfType for the same result −
ob.GetType().IsInstanceOfType(otherOb)