KeyedObjects data = new KeyedObjects();
data.addObject("A", new Double(1.0));
data.addObject("B", new Double(2.0));
data.addObject("C", new Double(3.0));
data.addObject("D", null);
// check key order
assertEquals(data.getKey(0), "A");
assertEquals(data.getKey(1), "B");
assertEquals(data.getKey(2), "C");