PairNeuronDouble should not implement Comparable.

As the purpose was only to sort neurons according to an associated
value, using an explicit comparator is simpler. Implementing Comparable
induces also implementing equals and hashcode which are not really
meaningful. They are nevertheless required by our code quality checking
tools.

src/main/java/org/apache/commons/math3/ml/neuralnet/MapUtils.java

@@ -20,6 +20,7 @@ package org.apache.commons.math3.ml.neuralnet;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Comparator;
 import java.util.HashMap;
 import java.util.List;
 
@@ -136,7 +137,13 @@ public class MapUtils {
             list.add(new PairNeuronDouble(n, d));
         }
 
-        Collections.sort(list);
+        Collections.sort(list, new Comparator<PairNeuronDouble>() {
+            /** {@inheritDoc} */
+            @Override
+            public int compare(final PairNeuronDouble pn1, final PairNeuronDouble pn2) {
+                return Double.compare(pn1.getValue(), pn2.getValue());
+            }
+        });
 
         final int len = list.size();
         final Neuron[] sorted = new Neuron[len];
@@ -292,7 +299,7 @@ public class MapUtils {
     /**
      * Helper data structure holding a (Neuron, double) pair.
      */
-    private static class PairNeuronDouble implements Comparable<PairNeuronDouble> {
+    private static class PairNeuronDouble {
         /** Key */
         private final Neuron neuron;
         /** Value */
@@ -317,26 +324,6 @@ public class MapUtils {
             return value;
         }
 
-        /** {@inheritDoc} */
-        public int compareTo(PairNeuronDouble other) {
-            return Double.compare(this.value, other.value);
-        }
-
-        /** {@inheritDoc} */
-        @Override
-        public boolean equals(Object other) {
-            if (!(other instanceof PairNeuronDouble)) {
-                return false;
-            }
-            return Double.doubleToRawLongBits(value) ==
-                   Double.doubleToRawLongBits(((PairNeuronDouble) other).value);
-        }
-
-        /** {@inheritDoc} */
-        @Override
-        public int hashCode() {
-            return Double.valueOf(value).hashCode();
-        }
-
     }
+
 }