Docs: Add Javadoc

CityDoctorParent/CityDoctorValidation/src/main/java/de/hft/stuttgart/citydoctor2/check/Checker.java

@@ -47,6 +47,7 @@ import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
 
+import javax.annotation.Nullable;
 import javax.xml.XMLConstants;
 import javax.xml.transform.Result;
 import javax.xml.transform.Source;
@@ -77,7 +78,6 @@ import de.hft.stuttgart.citydoctor2.datastructure.CityDoctorModel;
 import de.hft.stuttgart.citydoctor2.datastructure.CityObject;
 import de.hft.stuttgart.citydoctor2.datastructure.FeatureType;
 import de.hft.stuttgart.citydoctor2.datastructure.GmlId;
-import de.hft.stuttgart.citydoctor2.datastructure.ImplicitGeometryHolder;
 import de.hft.stuttgart.citydoctor2.parser.CityGmlConsumer;
 import de.hft.stuttgart.citydoctor2.parser.CityGmlParseException;
 import de.hft.stuttgart.citydoctor2.parser.CityGmlParser;
@@ -741,8 +741,22 @@ public class Checker {
         }
     }
 
+    /**
+     * Runs the validation on a list of Features. The checks are run asynchronously and multithreaded. Returns a list
+     * of {@link Future Futures} for evaluation if Features failed to be checked due to exceptions or failing to load from
+     * the cache. If failed, the respective Future will return the affected Feature's GmlID.
+     * <p>Checks finding an error in a Feature, or not having their dependencies met, are not a check-failure in this
+     * context.<p/>
+     * @param exec the threadpool for the tasks
+     * @param cache the cache of the model
+     * @param ids the list of GmlIds to check
+     * @param checkedCount the number of already checked Features for tracking the total progress of validation across retries
+     * @param l a listener for the progress of the validation, can be null
+     * @return a list of Futures containing the GmlId of Features that failed to execute all checks, and contain null otherwise
+     * @throws InterruptedException if interrupted while invoking the tasks for checking
+     */
     private List<Future<GmlId>> runChecksOnFeatures(ExecutorService exec, CityObjectCache cache, List<GmlId> ids, AtomicInteger checkedCount,
-                                            ProgressListener l)
+                                           @Nullable ProgressListener l)
             throws InterruptedException {
         float featureSum = ids.size() + (float) checkedCount.get();