Haskell style memoization in Java

I know this is heresy, but I tried to translate the examples from http://www.haskell.org/haskellwiki/Memoization to Java. So far I have:

public abstract class F<A,B> {
    public abstract B f(A a);
}

...
public static <A, B> F<A, B> memoize(final F<A, B> fn) {
  return new F<A, B>() {

    private final Map<A, B> map = new HashMap<A, B>();

    public B f(A a) {
      B b = map.get(a);
        if (b == null) {
          b = fn.f(a);
          map.put(a, b);
        }
      return b;
    }
  };
}

//usage:
private class Cell<X> {
    public X value = null;
}

...
final Cell<F<Integer, BigInteger>> fibCell = new Cell<F<Integer, BigInteger>>();
fibCell.value = memoize(new F<Integer, BigInteger>() {
  public BigInteger f(Integer a) {
     return a <= 1 ? BigInteger.valueOf(a) : fibCell.value.f(a - 1).add(fibCell.value.f(a - 2));
  }
});
System.out.println(fibCell.value.f(1000));

That works fine. Now I tried to implement the memoFix combinator defined as

memoFix :: ((a -> b) -> (a -> b)) -> a -> b
memoFix f =
   let mf = memoize (f mf) in mf

But I got stuck. Does this even make sense in Java, especially concerning its inherent lack of lazyness?