Q:

Programs with Collections.sort

I have a problem with Collections.sort I cannot solve.
I use a custom comparator to compare integers hashtable-based:
public class HashtableComparator<T> implements Comparator<T> {

public HashtableComparator(Map<T,Double> mapScore)
{
    this.mapScore=mapScore;
}
@Override
public int compare(T o1, T o2) {
    // TODO Auto-generated method stub
    double d1=mapScore.get(o1);
    double d2=mapScore.get(o2);

    if (d1<d2)
        return -1;
    else if (d2>d1)
        return 1;
    return 0;
}

public double getScore(T t)
{
    return mapScore.get(t);
}

private Map<T,Double> mapScore;
}

Now I sort the numbers by:
public static void main(String[] args)
{
  HashMap<Integer,Double> map=new HashMap<Integer,Double>();

  ArrayList<Integer> li=new ArrayList<Integer>();
  Random rn=new Random();
  for (int i=0;i<200;i++)
  {
    li.add(i);
    double r=rn.nextDouble();
    map.put(i, r);
  }
  ArrayList<Integer> li2=new ArrayList<Integer>();
  HashtableComparator<Integer> htComparator=
    new HashtableComparator<Integer>(map);

  Collections.sort(li,htComparator);
  for (Integer i1: li)
  {
    System.out.println("i: "+i1+": "+map.get(i1));
 }
 }

The output looks like this:
...
i: 154: 0.9367974470241198
i: 167: 0.9426082679825352
i: 158: 0.9530518486042212
i: 172: 0.9700636428116204
i: 174: 0.9979504046750738
i: 184: 0.011633259785655103
i: 187: 0.03498090300936352
i: 197: 0.07038500463581565
i: 181: 0.07821108293051438
i: 178: 0.12297017501683705
...
completely nonsensen.
Could someone give me a hint what is going wrong there?
Thanks
====
Tim

A:

Instead of writing your own comparison logic, try this:
    @Override
    public int compare(T o1, T o2) {
       Double d1 = mapScore.get(o1);
       Double d2 = mapScore.get(o2);
       return d1.compareTo(d2);
   }

because the Double wrapper class implements the Comparable interface.

