MATH-1279

Check precondition.
Thanks to David Georg Reichelt for the report.

src/changes/changes.xml

@@ -54,6 +54,9 @@ If the output is not quite correct, check for invisible trailing spaces!
     </release>
 
     <release version="4.0" date="XXXX-XX-XX" description="">
+      <action dev="erans" type="fix" issue="MATH-1279"> <!-- backported to 3.6 -->
+        Check precondition (class "o.a.c.m.random.EmpiricalDistribution").
+      </action>
       <action dev="erans" type="add" issue="MATH-1278"> <!-- backported to 3.6 -->
         Deep copy of "Network" (package "o.a.c.m.ml.neuralnet") to allow evaluation of
         of intermediate states during training.

src/main/java/org/apache/commons/math4/random/EmpiricalDistribution.java

@@ -37,6 +37,7 @@ import org.apache.commons.math4.exception.MathInternalError;
 import org.apache.commons.math4.exception.NullArgumentException;
 import org.apache.commons.math4.exception.OutOfRangeException;
 import org.apache.commons.math4.exception.ZeroException;
+import org.apache.commons.math4.exception.NotStrictlyPositiveException;
 import org.apache.commons.math4.exception.util.LocalizedFormats;
 import org.apache.commons.math4.stat.descriptive.StatisticalSummary;
 import org.apache.commons.math4.stat.descriptive.SummaryStatistics;
@@ -147,7 +148,8 @@ public class EmpiricalDistribution extends AbstractRealDistribution {
     /**
      * Creates a new EmpiricalDistribution with the specified bin count.
      *
-     * @param binCount number of bins
+     * @param binCount number of bins. Must be strictly positive.
+     * @throws NotStrictlyPositiveException if {@code binCount <= 0}.
      */
     public EmpiricalDistribution(int binCount) {
         this(binCount, new RandomDataGenerator());
@@ -157,8 +159,9 @@ public class EmpiricalDistribution extends AbstractRealDistribution {
      * Creates a new EmpiricalDistribution with the specified bin count using the
      * provided {@link RandomGenerator} as the source of random data.
      *
-     * @param binCount number of bins
+     * @param binCount number of bins. Must be strictly positive.
      * @param generator random data generator (may be null, resulting in default JDK generator)
+     * @throws NotStrictlyPositiveException if {@code binCount <= 0}.
      * @since 3.0
      */
     public EmpiricalDistribution(int binCount, RandomGenerator generator) {
@@ -180,12 +183,16 @@ public class EmpiricalDistribution extends AbstractRealDistribution {
      * Private constructor to allow lazy initialisation of the RNG contained
      * in the {@link #randomData} instance variable.
      *
-     * @param binCount number of bins
+     * @param binCount number of bins. Must be strictly positive.
      * @param randomData Random data generator.
+     * @throws NotStrictlyPositiveException if {@code binCount <= 0}.
      */
     private EmpiricalDistribution(int binCount,
                                   RandomDataGenerator randomData) {
         super(randomData.getRandomGenerator());
+        if (binCount <= 0) {
+            throw new NotStrictlyPositiveException(binCount);
+        }
         this.binCount = binCount;
         this.randomData = randomData;
         binStats = new ArrayList<SummaryStatistics>();

src/test/java/org/apache/commons/math4/random/EmpiricalDistributionTest.java

@@ -35,6 +35,7 @@ import org.apache.commons.math4.distribution.RealDistributionAbstractTest;
 import org.apache.commons.math4.distribution.UniformRealDistribution;
 import org.apache.commons.math4.exception.MathIllegalStateException;
 import org.apache.commons.math4.exception.NullArgumentException;
+import org.apache.commons.math4.exception.NotStrictlyPositiveException;
 import org.apache.commons.math4.random.EmpiricalDistribution;
 import org.apache.commons.math4.random.RandomGenerator;
 import org.apache.commons.math4.stat.descriptive.SummaryStatistics;
@@ -85,6 +86,12 @@ public final class EmpiricalDistributionTest extends RealDistributionAbstractTes
         }
     }
 
+    // MATH-1279
+    @Test(expected=NotStrictlyPositiveException.class)
+    public void testPrecondition1() {
+        new EmpiricalDistribution(0);
+    }
+
     /**
      * Test EmpiricalDistrbution.load() using sample data file.<br>
      * Check that the sampleCount, mu and sigma match data in