Add object factories to ISelection interface

Currently creating a IStructuredSelection requires to reference a
concrete implementing class, also handling null is explicitly required
and only List or Array are supported.

This adds some new object factory methods similar to what users are used
to with the Optional.of(...) / List.of(...) and similar and adds some
usages of the new methods.

bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceDialog.java

@@ -47,7 +47,6 @@
 import org.eclipse.jface.viewers.ISelectionChangedListener;
 import org.eclipse.jface.viewers.IStructuredSelection;
 import org.eclipse.jface.viewers.SelectionChangedEvent;
-import org.eclipse.jface.viewers.StructuredSelection;
 import org.eclipse.jface.viewers.TreeViewer;
 import org.eclipse.jface.viewers.ViewerComparator;
 import org.eclipse.jface.viewers.ViewerFilter;
@@ -953,7 +952,7 @@ void selectCurrentPageAgain() {
 		if (lastSuccessfulNode == null) {
 			return;
 		}
-		getTreeViewer().setSelection(new StructuredSelection(lastSuccessfulNode));
+		getTreeViewer().setSelection(IStructuredSelection.of(lastSuccessfulNode));
 		currentPage.setVisible(true);
 	}
 
@@ -987,7 +986,7 @@ protected void selectSavedItem() {
 			}
 		}
 		if (node != null) {
-			getTreeViewer().setSelection(new StructuredSelection(node), true);
+			getTreeViewer().setSelection(IStructuredSelection.of(node), true);
 			// Keep focus in tree. See bugs 2692, 2621, and 6775.
 			getTreeViewer().getControl().setFocus();
 		}

bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ColumnViewer.java

@@ -410,7 +410,7 @@ public void editElement(Object element, int column) {
 				getControl().setRedraw(false);
 				// Set the selection at first because in Tree's
 				// the element might not be materialized
-				setSelection(new StructuredSelection(element), true);
+				setSelection(IStructuredSelection.of(element), true);
 
 				Widget item = findItem(element);
 				if (item != null) {
@@ -1082,7 +1082,7 @@ ISelection getUpdatedSelection(ISelection selection) {
 				}
 			}
 			if (found) {
-				return new StructuredSelection(list);
+				return IStructuredSelection.of(list);
 			}
 		}
 		// by default return given selection.

bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ComboBoxViewerCellEditor.java

@@ -173,11 +173,7 @@ public LayoutData getLayoutData() {
 	protected void doSetValue(Object value) {
 		Assert.isTrue(viewer != null);
 		selectedValue = value;
-		if (value == null) {
-			viewer.setSelection(StructuredSelection.EMPTY);
-		} else {
-			viewer.setSelection(new StructuredSelection(value));
-		}
+		viewer.setSelection(IStructuredSelection.ofNullable(value));
 	}
 
 	/**

bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/IStructuredSelection.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2023 IBM Corporation and others.
+ * Copyright (c) 2000, 2024 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -11,9 +11,11 @@
  * Contributors:
  *     IBM Corporation - initial API and implementation
  *     Christoph Läubrich - add support for stream() method
+ *                        - add support for factory methods
  *******************************************************************************/
 package org.eclipse.jface.viewers;
 
+import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
 import java.util.stream.Stream;
@@ -71,4 +73,72 @@ public interface IStructuredSelection extends ISelection, Iterable {
 	default Stream<Object> stream() {
 		return StreamSupport.stream(spliterator(), false);
 	}
+
+	/**
+	 * Creates a new {@link IStructuredSelection} wrapping the possibly
+	 * <code>null</code> object.
+	 *
+	 * @param obj the element (might be <code>null</code>) to create a
+	 *            {@link IStructuredSelection} from.
+	 * @return a {@link IStructuredSelection} with this single element, or an empty
+	 *         selection if the object is <code>null</code>
+	 */
+	static <E> IStructuredSelection ofNullable(E obj) {
+		if (obj == null) {
+			return StructuredSelection.EMPTY;
+		}
+		return new StructuredSelection(obj);
+
+	}
+
+	/**
+	 * Creates a new {@link IStructuredSelection} wrapping the given object.
+	 *
+	 * @param obj the element (must not be <code>null</code>) to create a single
+	 *            element {@link IStructuredSelection} from it.
+	 * @return a {@link IStructuredSelection} with this single element
+	 */
+	static <E> IStructuredSelection of(E obj) {
+		return new StructuredSelection(obj);
+	}
+
+	/**
+	 * Created a new {@link IStructuredSelection} containing the given object
+	 *
+	 * @param objects the object to contain in the selection
+	 * @return a {@link IStructuredSelection} containing the given elements
+	 */
+	@SafeVarargs
+	static <E> IStructuredSelection of(E... objects) {
+		if (objects.length == 0) {
+			return StructuredSelection.EMPTY;
+		}
+		return new StructuredSelection(objects);
+	}
+
+	/**
+	 * create a new {@link IStructuredSelection} using the given collection
+	 *
+	 * @param collection
+	 * @return a {@link IStructuredSelection} containing the elements of the
+	 *         collection
+	 */
+	static <E> IStructuredSelection of(Collection<E> collection) {
+		if (collection.isEmpty()) {
+			return StructuredSelection.EMPTY;
+		}
+		if (collection instanceof List<?> list) {
+			return new StructuredSelection(list);
+		}
+		return new StructuredSelection(collection.toArray(), false);
+	}
+
+	/**
+	 * Returns an empty {@link IStructuredSelection}
+	 *
+	 * @return a {@link IStructuredSelection} that is empty.
+	 */
+	static IStructuredSelection empty() {
+		return StructuredSelection.EMPTY;
+	}
 }

bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredSelection.java

@@ -68,9 +68,17 @@ public StructuredSelection() {
 	 * @param elements an array of elements
 	 */
 	public StructuredSelection(Object[] elements) {
+		this(elements, true);
+	}
+
+	StructuredSelection(Object[] elements, boolean copy) {
 		Assert.isNotNull(elements);
-		this.elements = new Object[elements.length];
-		System.arraycopy(elements, 0, this.elements, 0, elements.length);
+		if (copy) {
+			this.elements = new Object[elements.length];
+			System.arraycopy(elements, 0, this.elements, 0, elements.length);
+		} else {
+			this.elements = elements;
+		}
 		this.comparer = null;
 	}
 

bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java

@@ -1083,7 +1083,7 @@ protected void handleDoubleSelect(SelectionEvent event) {
 			// For details, see bug 90161 [Navigator] DefaultSelecting folders shouldn't always expand first one
 			ISelection selection;
 			if (event.item != null && event.item.getData() != null) {
-				selection = new StructuredSelection(event.item.getData());
+				selection = IStructuredSelection.of(event.item.getData());
 			}
 			else {
 				selection = getSelection();