Bug 201906 [Viewers] 3.4 ColumnViewerEditor leaks ViewerCell instances.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ColumnViewerEditor.java
import org.eclipse.core.runtime.ListenerList;
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.FocusAdapter;
import org.eclipse.swt.events.FocusEvent;
import org.eclipse.swt.events.FocusListener;
import org.eclipse.swt.events.MouseAdapter;
import org.eclipse.swt.events.MouseEvent;
import org.eclipse.swt.events.MouseListener;
import org.eclipse.swt.events.TraverseEvent;
import org.eclipse.swt.events.TraverseListener;
import org.eclipse.swt.widgets.Control;
import org.eclipse.swt.widgets.Item;
/**
 * This is the base for all editor implementations of Viewers. ColumnViewer
 * implementors have to subclass this class and implement the missing methods
 *
 * @since 3.3
 * @see TableViewerEditor
 * @see TreeViewerEditor
 */
public abstract class ColumnViewerEditor {
	private CellEditor cellEditor;
	private ICellEditorListener cellEditorListener;
	private FocusListener focusListener;
	private MouseListener mouseListener;
	private ColumnViewer viewer;
	private TraverseListener tabeditingListener;
	private ViewerCell cell;
	private ListenerList editorActivationListener;
	private ColumnViewerEditorActivationStrategy editorActivationStrategy;