Are your ranges non-overlapping? If so you could use a TreeMap:
TreeMap<Double, Character> m = new TreeMap<Double, Character>();
m.put(1.0, 'A');
m.put(2.9, null);
m.put(4.0, 'B');
m.put(6.0, null);
m.put(6.5, 'C');
m.put(10.0, null);
The lookup logic is a bit complicated by the fact that you probably want an inclusive lookup (i.e. 2.9 maps to ‘A’, and not undefined):
private static <K, V> V mappedValue(TreeMap<K, V> map, K key) {
Entry<K, V> e = map.floorEntry(key);
if (e != null && e.getValue() == null) {
e = map.lowerEntry(key);
}
return e == null ? null : e.getValue();
}
Example:
mappedValue(m, 5) == 'B'
More results include:
0.9 null
1.0 A
1.1 A
2.8 A
2.9 A
3.0 null
6.4 null
6.5 C
6.6 C
9.9 C
10.0 C
10.1 null