Backed Collections: Sorted Map subMap

[John Paterson]

Hi Folks,

I have a question with regards to Sorted Map's subMap method. Do have a look at the following code, my question follows:

import java.util.*;

public class BackedCollection {

    public static void main(String[] args) {

        TreeMap<String, String> map = new TreeMap<String, String>();
        map.put("a", "ant");
        map.put("d", "dog");
        map.put("h", "horse");

        SortedMap<String, String> submap;
        submap = map.subMap("b", "g"); //Highlight

        System.out.println(map + " " + submap); 

           }
}

The output for the above is:

{a=ant, d=dog, h=horse} {d=dog}

If I were to change the line, in which I have made the comment 'Highlight' to

submap = map.subMap("b", "d")

The output from the second print statement is than

{}

I don't understand than why? I was actually still expecting to get the same output as before.

I am saying this based on my understanding that the subMap method works as follows:

Content: a d h
KeyValue: a, b, c, d, e, f, g, h, i, j, k, l, m, n

Since I had ("b" and "d") I thought I should still get {d=dog}. I hope someone can point out to me where I am going wrong. Thanks.

regards
John

[Winston Gutkowski]

John Paterson wrote:Since I had ("b" and "d") I thought I should still get {d=dog}. I hope someone can point out to me where I am going wrong.

As they say: when all else fails, read the instructions.

SortedMap.submap()'s documentation says, quite specifically:
"...Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive..."

HIH

Winston

[Edit] BTW, most Java methods that return "ranges" behave this way. cf: String.substring().

[Rob Spoor]

Even if the toKey is inclusive, "d" is smaller than "dog". The method doesn't just look at the first character - it checks if toKey.compareTo(k) >= 0 for each key k until this check returns false. "d".compareTo("dog") returns something < 0.