HasSet vs ArrayList and modelling issue

[mickey0]

Hello,

I must implement a class MyMethod; read a method declaration from a file with a parser, and while parsing I must fill that MyMethod Object.

Now, at the moment this my objects are in this fashion:

//allow me all public to reduce code verbosity
class MyMethod {
           public Signature s;
           public  String returnedType;
}
class MySignature {
      public String name;
      //public  List<MyVar> vars = new ArrayList<Var>();  
        public  Set<MyVar> vars = new LinkedHashSet<MyVar>();  //eg, (int x, String s, int y)'
}
class MyVar {    //eg. 'int x'
       public String id;  
       public String type;
}

Now, in MySignature I used a Linked hashSet because I want to keep the order of insertion (and I know that I can't have two params with the same ID, here overrivde properly) since the Parser parser the list of parameters in the order they are written.
I want to keep a position field because I would like, given an id (eg, 'x'), find its position within a certain signature WITHOUT iterate over all list of parameters (I suppose this is slower). So:
- was it better to iterate on it (and better declare it as ArrayList) ? using arrayList I could avoid the position "problem", since I can retrieve it from iterating on the List.
- assuming to really need the position, where could I put it ? Within MyVar?
- assuming to use the Set, how can I override equals in MyVar to cope this situation (ie. no at most one MyVar with a certain Id)

thanks.