Ranges

Main.java

import java.util.Map.Entry;
import java.util.TreeMap;

// See http://stackoverflow.com/a/13400317/611182
public class Main {

    private static TreeMap<Double, String> m = new TreeMap<Double, String>();
    static {
        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);
    }

    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();
    }


    private static final double[] testValues = new double[] {
        0.9,
        1.0,
        1.1,
        2.8,
        2.9,
        3.9,
        4.0,
        4.1,
        5.9,
        6.0,
        6.1,
        6.4,
        6.5,
        6.6,
        9.9,
        10.0,
        10.1
    };

    public static void main(String[] args) {
        for (double d : testValues) {
            System.out.println(d + " " + mappedValue(m, d));
        }
    }

}

0.9 null
1.0 A
1.1 A
2.8 A
2.9 A
3.9 null
4.0 B
4.1 B
5.9 B
6.0 B
6.1 null
6.4 null
6.5 C
6.6 C
9.9 C
10.0 C
10.1 null