protected final Interaction findInteraction(String id) {
        for(Node n= interactions.head(), end= interactions.tail(); (n= n.next()) != end;) {
            Interaction i= (Interaction)n.value();
            
            if(i.id.equals(id)) {
                return i;
            }
        }
        
        return null;
    }
protected final Interaction findInteraction ( String id ) { for ( Node n = interactions . head ( ) , end = interactions . tail ( ) ; ( n = n . next ( ) ) != end ; ) { Interaction i = ( Interaction ) n . value ( ) ; if ( i . id . equals ( id ) ) { return i ; } } return null ; }
Caller must hold the lock on interactions!