Bug 5774 Unpredicatable behaviour on double click in packages view
from EC: If you double click a file in the packages view, it opens the file (technically, compilation unit I believe) -- if not already open. However, if the file is already open, a single click selects it as the active editor tag; a double click expands its structure in the packages view. This is unpredictable behavior ;
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
/**
	 * Answer the property defined by key.
	 */
	public Object getAdapter(Class key) {
		if (key.equals(ISelectionProvider.class))
			return fViewer;
		return super.getAdapter(key);
	}
	/**
	 * Returns the tool tip text for the given element.
	 */
	String getToolTipText(Object element) {
		String result;
		if (!(element instanceof IResource)) {
			result= ((ILabelProvider) getViewer().getLabelProvider()).getText(element);
		} else {
			IPath path= ((IResource) element).getFullPath();
			if (path.isRoot()) {
				result= PackagesMessages.getString("PackageExplorer.title"); 
			} else {
				result= path.makeRelative().toString();
			}
		}
		IWorkingSet ws= fWorkingSetFilter.getWorkingSet();
		if (ws == null)
			return result;
		String wsstr= "Working Set: "+ws.getName();
		if (result.length() == 0)
			return wsstr;