Bug 21631 JavaUI.createTypeDialog() should provide default message [dialogs]
2.0 Release If you use JavaUI.createTypeDialog() to create a new (single selection) type dialog, and then open the dialog, the open will fail silently. The dialog cannot be succesfully opened unless you send setMessage() to the dialog before you open it. This behaviour should be documented, or, preferably, a default message ("Please select a type/class/interface") should be provided.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/JavaUI.java
*   <code>CONSIDER_EXTERNAL_JARS</code>, or their bitwise OR, or <code>0</code>
	 * @param multipleSelection <code>true</code> if multiple selection is allowed
	 * @return a new selection dialog
	 */
	public static SelectionDialog createMainTypeDialog(Shell parent, IRunnableContext context, IJavaSearchScope scope, int style, boolean multipleSelection) {
		return createMainTypeDialog(parent, context, scope, style, multipleSelection, "");
	}
	
	/**
	 * Creates a selection dialog that lists all types in the given project.
	 * The caller is responsible for opening the dialog with <code>Window.open</code>,
	 * and subsequently extracting the selected type(s) (of type
	 * <code>IType</code>) via <code>SelectionDialog.getResult</code>.
	 * 
	 * @param parent the parent shell of the dialog to be created
	 * @param context the runnable context used to show progress when the dialog
	 *   is being populated
	 * @param project the Java project
	 * @param style flags defining the style of the dialog; the only valid values are
	 *   <code>IJavaElementSearchConstants.CONSIDER_CLASSES</code>,
	 *   <code>CONSIDER_INTERFACES</code>, or their bitwise OR 
	 *   (equivalent to <code>CONSIDER_TYPES</code>)
	 * @param multipleSelection <code>true</code> if multiple selection is allowed
	 * @return a new selection dialog
	 * @exception JavaModelException if the selection dialog could not be opened
	 */
	public static SelectionDialog createTypeDialog(Shell parent, IRunnableContext context, IProject project, int style, boolean multipleSelection) throws JavaModelException {
		IJavaSearchScope scope= SearchEngine.createJavaSearchScope(new IJavaProject[] { JavaCore.create(project) });
		return createTypeDialog(parent, context, scope, style, multipleSelection);
	}