TreeMap Insanity (or is that me?)

[Mike Curwen]

Map result = selectMap(query, true);

Iterator i = result.keySet().iterator();
while (i.hasNext()) {
System.out.println("key: " + i.next());
}

My selectMap() method returns a TreeMap. I've confirmed that the keys are being placed into the TreeMap *in order* (not that that should matter). When I then retrieve the keySet and try to iterate over them, I find that their "natural order" seems to be wacky.

key: 9
key: 8
key: 7
key: 16
key: 6
key: 15
key: 5
key: 14
key: 4
key: 13
key: 3
key: 12
key: 2
key: 1
key: 11
key: 10

Starting at the bottom, read the numbers from right to left. (imagine you're reading them in a mirror)
01
11
1
2
21
etc...

The same thing happens when I try to get values() to get a Collection view. From the API:

Returns a collection view of the values contained in this map. 
The collection's iterator will return the values in the order that 
their corresponding keys appear in the tree

But in fact, it's in the same order as shown above (only the output is the 'value' part of the TreeMap and not the key)


What is going on? Is the "natural order" of Strings (as implemented by String's default Comparator) like this?

I think not, but what else could be happening?
[ April 05, 2003: Message edited by: Mike Curwen ]

[Michael Morris]

Hi Mike,
Umm, very strange. I ran a test and got the expected ASCII sort:

import java.util.*;
public class TreeMapTest {
    public Map getSortedMap(Object[] keys, Object[] values) {
        Map map = new TreeMap();
        for (int i = 0; i < keys.length; i++) {
            map.put(keys[i], values[i]);
        }
        return map;
    }
    public static void main(String[] args) {
        TreeMapTest tmt = new TreeMapTest();
        String[] keys   = {"1",  "2",  "3",  "4",  "5",  "6",  "7",  "8",
                           "9", "10", "11", "12", "13", "14", "15", "16"};
        String[] values = {"A",  "B",  "C",  "D",  "E",  "F",  "G",  "H",
                           "I", "AA", "BB", "CC", "DD", "EE", "FF", "GG"};
        Map map = tmt.getSortedMap(keys, values);
        Iterator i = map.keySet().iterator();
        while (i.hasNext()) {
            System.out.println("key: " + i.next());
        }
    }
}

Output:

key: 1
key: 10
key: 11
key: 12
key: 13
key: 14
key: 15
key: 16
key: 2
key: 3
key: 4
key: 5
key: 6
key: 7
key: 8
key: 9

I guess you've checked that your keys are for sure Strings. Also, could it be an encoding problem? Perhaps with an encoding that reads right to left.
Michael Morris

[Mike Curwen]

Here's the full code:

public static Map selectMap(String query_string, boolean ordered) {
Map returnVal = null;
if (ordered) {
logger.debug("***TreeMap");
returnVal = new TreeMap();
} else {
logger.debug("***HashMap");
returnVal = new HashMap();
}
try {
Connection con = provider.getConnection();
Statement st= con.createStatement();
ResultSet rs = st.executeQuery(query_string);
ResultSetMetaData rsmd = rs.getMetaData();
int numberOfColumns = rsmd.getColumnCount();
returnVal = new HashMap(numberOfColumns);                           //1
while (rs.next()) {
     logger.debug(rs.getString(1) + ": " + rs.getString(2));
     returnVal.put(new Long(rs.getLong(1)) + "", rs.getString(2)); //2
}
provider.releaseConnection(con);
} catch (Exception e) {
logger.error(e);
}
return returnVal;
}

Two things of note here.
//2 The extra "" was in fact turning it back into a String. If I removed the "", then I'd get a sorted result in DESCENDING order.

The real problem.... //1 DUH! It's a HashMap again! This is the type of thing that happens a lot when you 'improve' code, right? (the method didn't used to take a boolean 'sorted' parameter).
[ April 06, 2003: Message edited by: Mike Curwen ]
[ April 06, 2003: Message edited by: Mike Curwen ]

[Jim Yingst]

So, problem solved now?

[Mike Curwen]

Yup. I was checking at the top of my method to see if I should make a HashMap or TreeMap, but then later on (at //2) I go ahead and make it a HashMap.
[ April 06, 2003: Message edited by: Mike Curwen ]