Sublis in Java

public static Object
  sublis(Cons alist, Object tree) {
    if ( consp(tree) )
      return cons(sublis(alist,
                         first((Cons) tree)),
           (Cons) sublis(alist,
                         rest((Cons) tree)));
    if ( tree == null ) return null;
    Cons pair = assoc(tree, alist);
    return ( pair == null ) ? tree
                            : second(pair); }