TreeMap/Comparator a mapping problem

Hi,
  When I run the following code
 several output lines are not what I expect.

I expect:
1:1:7 [red, red]
1:32:18 [yellow]
7:11:20 [orange]

but get:
1:1:7 Why is dataByCoordinate.get(k)==null here?
1:32:18 Why is dataByCoordinate.get(k)==null here?
7:11:20 Why is dataByCoordinate.get(k)==null here?

Is there something wrong with my CoordinateComparator?
Do I not understand how TreeMap works?
Something else?
Is there an easier/better way of mapping my input to output?

Can I safely ignore the warning: Type safety: The expression
of type TestMapping.CoordinateComparator needs unchecked
conversion to conform to Comparator<? super String>

Thanks
Jeff Higgins

import java.util.ArrayList;
import java.util.Comparator;
import java.util.TreeMap;

public class TestMapping {

  public static void main(String[] args)
  {
    ArrayList<String> metCriteria = new ArrayList<String>();
    metCriteria.add("black 1:1:1 1:1:1 1:1:2 1:1:2 1:1:3 13:13:1");
    metCriteria.add("brown 13:13:1 14:20:21 16:5:7");
    metCriteria.add("red 1:1:1 1:1:2 1:1:2 1:1:3 1:1:3 1:1:3 1:1:4" +
    " 1:1:5 1:1:5 1:1:6 1:1:7 1:1:7 13:13:1 24:49:7");
    metCriteria.add("orange 5:32:37 7:11:20 7:20:36 12:18:5 19:13:5");
    metCriteria.add("yellow 1:7:14 1:32:18");
    metCriteria.add("green 24:49:7 41:16:14");
    metCriteria.add("blue 2:38:18 19:13:5");
    metCriteria.add("violet 19:13:5 24:49:7 42:24:31 72:3:19");
    metCriteria.add("gray 1:2:6 44:13:11 61:2:17 70:2:4");
    metCriteria.add("white 1:2:6 9:9:9");

    TreeMap<String,ArrayList<String>> dataByCoordinate =
      new TreeMap<String,ArrayList<String>>(
          new CoordinateComparator());

    for(String line : metCriteria)
    {
      String[] a = line.split(" ",2);
      String[] b = a[1].split(" ");
      for(int i = 0; i < b.length; i++)
        if(dataByCoordinate.containsKey(b[i]))
        {
          dataByCoordinate.get(b[i]).add(a[0]);
        }
        else
        {
          dataByCoordinate.put(b[i], new ArrayList<String>());
          dataByCoordinate.get(b[i]).add(a[0]);
        }
    }
    for(String k : dataByCoordinate.keySet())
    {
      if(dataByCoordinate.get(k) != null)
      {
        System.out.println(k + " " +
          dataByCoordinate.get(k).toString());
      }
      else
      {
        System.out.println(k +
          " Why is dataByCoordinate.get(k)==null here?");
      }
    }

  }

  static class CoordinateComparator implements Comparator
  {
    public final int compare ( Object o1, Object o2 )
    {
      String s1 = ((String) o1);
      String s2 = ((String) o2);

      String[] sa = s1.split(":");
      long[] a = new long[3];
      a[0] = Long.valueOf(sa[0]);
      a[1] = Long.valueOf(sa[1]);
      a[2] = Long.valueOf(sa[2]);

      String[] sb = s2.split(":");
      long[] b = new long[3];
      b[0] = Long.valueOf(sb[0]);
      b[1] = Long.valueOf(sb[1]);
      b[2] = Long.valueOf(sb[2]);

      long[] c = new long[3];
      c[0] = signum(a[0] - b[0]);
      c[1] = signum(a[1] - b[1]);
      c[2] = signum(a[2] - b[2]);

      if(c[0] < 0)
      {
        return -1;
      }
      else if(c[0]==0 && c[1]==0 && c[2]<0)
      {
        return -1;
      }
      else if(c[0]==0 && c[1]==0 && c[2]==0)
      {
        return 0;
      }
      else if(c[0]==0 && c[1]==0 && c[2]>0)
      {
        return 1;
      }
      else
      {
        return 1;
      }
    }

    static final int signum ( long diff )
    {
      if ( diff > 0 ) return 1;
      if ( diff < 0 ) return -1;
      else return 0;
    }
  }
}