Add explanation to CategoricalBarChart constructor.

src/main/java/de/tudresden/inf/mci/brailleplot/diagrams/BarChart.java

@@ -13,7 +13,7 @@ import java.util.stream.Collectors;
 /**
  * Representation of a bar chart with basic data functions. Implements Renderable.
  * @author Richard Schmidt, Georg Graßnick
- * @version 2019.07.29
+ * @version 2019.09.02
  */
 public class BarChart implements Renderable {
     private PointListContainer<PointList> mData;

src/main/java/de/tudresden/inf/mci/brailleplot/diagrams/CategoricalBarChart.java

@@ -6,13 +6,19 @@ import de.tudresden.inf.mci.brailleplot.datacontainers.PointList;
 /**
  * Representation of a bar chart composed from categories of multiple bars each. Implements Renderable.
  * @author Leonard Kupper
- * @version 2019.08.29
+ * @version 2019.09.02
  */
 public class CategoricalBarChart extends BarChart {
 
     private CategoricalPointListContainer<PointList> mData;
 
     public CategoricalBarChart(final CategoricalPointListContainer<PointList> data) {
+        /*
+            This constructor is supposed to create a bar chart with categories. Since it is just an extension of
+            the normal BarChart, the super() constructor is called first. The mData member is then set to "hide" the
+            parents PointListContainer member.
+            (Because the reference to the data of a CategoricalBarChart must be a CategoricalPointListContainer instead.)
+         */
         super(data);
         mData = data;
     }

src/main/java/de/tudresden/inf/mci/brailleplot/rendering/BarChartRasterizer.java

@@ -28,7 +28,7 @@ import static java.lang.Math.round;
  * A rasterizer for instances of {@link CategoricalBarChart} which is able to display multiple bars per category.
  * The rasterizer is 'cell' based, restricted to 6-dot layouts.
  * @author Leonard Kupper
- * @version 2019.08.29
+ * @version 2019.09.02
  */
 public class BarChartRasterizer implements Rasterizer<CategoricalBarChart> {