selectAll(): make private and return empty list instead of null

* Return empty list instead of null on unexpected input (null or wrong
  selection type)
* Fixes NPE in setSelection()

Issue-Ref: 3545
Issue-Url: https://af3-developer.fortiss.org/issues/3545



Signed-off-by: Simon Barner <barner@fortiss.org>

org.fortiss.tooling.kernel.ui/src/org/fortiss/tooling/kernel/ui/util/.ratings

@@ -7,7 +7,7 @@ EObjectSelectionUtils.java 128cf8f96c6b9478171dff3deda662d5934f5f44 GREEN
 KernelUIUtils.java 46d3279ef3523b104f89a6c526109f72d36f72f2 GREEN
 ObservableUtils.java 34abfd1dfaf9c0acbb31caf1f525e7b39416c116 GREEN
 PropertiesConstantUtils.java 59b1a1e4d594bb98db3aa396f2ff6474ba405920 GREEN
-SelectionUtils.java 3d20f87eaaee04173686ef62b09ca6971702cd00 GREEN
+SelectionUtils.java 33aec7cccccb28e5568140cf8e5443ce0f9f59f7 YELLOW
 TutorialUIServiceUtils.java 093a8a3549c6952d44ea508e66691434b17a95b5 GREEN
 UndoRedoImpl.java f218500875bda0ef52f4cc2ccdf452825e6751f7 GREEN
 WidgetsFactory.java 5be121cc81e93731f4d0ab11e7707417fa950c2c GREEN

org.fortiss.tooling.kernel.ui/src/org/fortiss/tooling/kernel/ui/util/SelectionUtils.java

@@ -15,9 +15,11 @@
 +--------------------------------------------------------------------------*/
 package org.fortiss.tooling.kernel.ui.util;
 
+import static java.util.Collections.emptyList;
 import static org.conqat.ide.commons.ui.ui.WorkbenchUtils.getActiveEditor;
+import static org.fortiss.tooling.common.util.LambdaUtils.filterByType;
 
-import java.util.ArrayList;
+import java.util.Collection;
 import java.util.List;
 
 import org.eclipse.emf.ecore.EObject;
@@ -90,29 +92,24 @@ public class SelectionUtils {
 	}
 
 	/**
-	 * Returns a list of all the selected elements that have the given type or
-	 * null if selection is null or is not an IStructuredSelection.
+	 * Returns a {@link Collection} of all the selected elements that have the given type (possibly
+	 * an empty list, in particular if {@code selection} is {@code null} or is not an
+	 * {@link IStructuredSelection}.
 	 * 
 	 * @param selection
 	 *            the current selection
 	 * @param type
 	 *            the type of elements to be returned
-	 * @return the list of elements of the given type
+	 * @return the {@link Collection} of elements of the given type
 	 */
 	@SuppressWarnings("unchecked")
-	public static <T> List<T> selectAll(ISelection selection, Class<T> type) {
+	private static <T> Collection<T> selectAll(ISelection selection, Class<T> type) {
 		if(selection == null || !(selection instanceof IStructuredSelection)) {
-			return null;
+			return emptyList();
 		}
 
 		IStructuredSelection structuredSelection = (IStructuredSelection)selection;
-		List<T> elements = new ArrayList<T>();
-		for(Object element : structuredSelection.toList()) {
-			if(type.isInstance(element)) {
-				elements.add((T)element);
-			}
-		}
-		return elements;
+		return filterByType(structuredSelection.toList(), type);
 	}
 
 	/**