HashMap problem: insert with hash code retrieve by index

Lets say we have the following class

public class Foo {
    private Map<Integer, String> dataMap = new HashMap<Integer,
String>();

    public String getValueAt(int idx) {
        // I wish I don't use for loop here ...
    }

    public void addValue(String s) {
        String l = dataMap.put(getHashCode(s), s);
    }
}

The problem is that I have to fill the map with values that are
absolutely inconsistent with each other, they are actually hash codes,
but when I call getValueAt method I need to get an element that would
be taken from Nth position.

Assume I have the following code

Foo f = new Foo();
f.addValue("qwerty");
f.addValue("12345");
// i know that the size of the HashMap is 2, so the following must be
fair
f.getValueAt(0); // OK
f.getValueAt(1); // OK
f.getValueAt(2); // ERROR - out of range

I do understand that the order of extraction in HashMap is unpredicted
- this is OK, but what is the best way to implement the functionality
that would help me extract elements from that map by an absolute index?