You may use the ClassMaker this way:

// ClassesMaker (double vMin, double vMax, int nClasses)
ClassesMaker cm = new ClassesMaker (1, 10, 2);
double w = cm.getClassWidth ();
int index = cm.whichClass (3.2);
double center = cm.getClassCenter (index);

The main method of ClassesMaker contains a test:

ClassesMaker vMin 1.0 vMax 10.0 nClasses 5 
EPSILON 1.0E-5 classWidth 1.8 classes limits 1 2.8 4.6 6.4 8.2 10 
class (1) 0
class (1.2) 0
class (5) 2
class (9) 4
class (10) 5
 
ClassesMaker vMin 2.0 vMax 10.0 nClasses 2 
EPSILON 1.0E-5 classWidth 4.0 classes limits 2 6 10 
cm.getClassWidth () 4.0
cm.whichClass (6.1) 1
cm.getClassCenter (1) 8.0

You may use the Classifier, itself based on the ClassMaker:

Collection list = new ArrayList ();
list.add (new Double (0));
list.add (new Double (1.1));
list.add (new Double (2));
list.add (new Double (8.1));
list.add (new Double (8.2));
list.add (new Double (10));
 
// Which value must be used for the objects in the list (other e.g. ((Tree) o).getDbh ())
ClassifierCriterion cc = new ClassifierCriterion() {
	@Override
	public double getValue (Object o) {
		return ((Double) o).doubleValue ();
	}
};
 
// min bound: 0, classWidth: 1
Classifier c = new Classifier (list, cc, 0, 1);
int rc = c.execute ();
 
System.out.println (c.toString ());
 
// Available methods:
c.getDistribution ();
c.getN ();
c.getMinLabels ();
c.getCenterLabels ();
c.getMaxLabels (); //...

What the Classifier.toString () method returns in this case:

Classifier vMin: 0.0 vMax: 11.0 classWidth: 1.0 n: 11
0.5 [0,1[: 1
1.5 [1,2[: 1
2.5 [2,3[: 1
3.5 [3,4[: 0
4.5 [4,5[: 0
5.5 [5,6[: 0
6.5 [6,7[: 0
7.5 [7,8[: 0
8.5 [8,9[: 2
9.5 [9,10[: 0
10.5 [10,11[: 1