map - Get values for keys within a range in Java

Question

Suppose I have a map in Java which looks like this:

{ 
 39:"39 to 41",
 41:"41 to 43",
 43:"43 to 45",
 45:">=45"
}

If the keys are in sorted order(either using treemap or linkedhashmap).Now if i try to get a value which is >=39 and <41.Then I should get the String "39 to 41".How do I do this efficiently?

Answer 1

It looks like you want more than a SortedMap; you want a NavigableMap! Specifically you can use the floorKey operation.

Here's an example:

    NavigableMap<Integer,String> map =
        new TreeMap<Integer, String>();

    map.put(0, "Kid");
    map.put(11, "Teens");
    map.put(20, "Twenties");
    map.put(30, "Thirties");
    map.put(40, "Forties");
    map.put(50, "Senior");
    map.put(100, "OMG OMG OMG!");

    System.out.println(map.get(map.floorKey(13)));     // Teens
    System.out.println(map.get(map.floorKey(29)));     // Twenties
    System.out.println(map.get(map.floorKey(30)));     // Thirties
    System.out.println(map.floorEntry(42).getValue()); // Forties
    System.out.println(map.get(map.floorKey(666)));    // OMG OMG OMG!

Note that there are also ceilingKey, lowerKey, higherKey, and also …Entry instead of …Key operations as well which returns a Map.Entry<K,V> instead of just the K.