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
/** 
	 * Initializes the default preferences
	 */
	public static void initDefaults(IPreferenceStore store) {
		store.setDefault(TAG_SHOWLIBRARIES, true);
		store.setDefault(TAG_SHOWBINARIES, true);
	}
	/**
	 * Returns the package explorer part of the active perspective. If 
	 * there isn't any package explorer part <code>null</code> is returned.
	 */
	public static PackageExplorerPart getFromActivePerspective() {
		IViewPart view= JavaPlugin.getActivePage().findView(VIEW_ID);
		if (view instanceof PackageExplorerPart)
			return (PackageExplorerPart)view;
		return null;	
	}
	
	/**
	 * Makes the package explorer part visible in the active perspective. If there
	 * isn't a package explorer part registered <code>null</code> is returned.
	 * Otherwise the opened view part is returned.
	 */
	public static PackageExplorerPart openInActivePerspective() {
		try {
			return (PackageExplorerPart)JavaPlugin.getActivePage().showView(VIEW_ID);
		} catch(PartInitException pe) {
			return null;
		}