ANTLR, lack of method in C# target

I generated the C# code from tree grammar using ANTLR and I cannot find the method downup(). Is the sequence of calls:

topdown();
bottomup();

equivalent to downup() method? Why the method does exist in Java but not in C#? And why do they (the authors) advise to override the following methods:

protected override void Topdown()开发者_如何学Python { topdown(); }
protected override void Bottomup() { bottomup(); }

whereas C# says there are no such methods to override?