Bug 33550 [Dialogs] Dialog should support remembering size and position
There are several dialogs that remember its size and position. Since restore the size and considering screen size and font changes isn't trivial JFace's Dialog class should support remembering and restoring size and position. These would realy ease the task for subclasses. May be you can steel the code from OpenTypeSelectionDialog.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/Dialog.java
* Returns the button created when <code>createButton</code> is called
     * with an ID of <code>IDialogConstants.CANCEL_ID</code>. If
     * <code>createButton</code> was never called with this parameter, or if
     * <code>createButton</code> is overridden, <code>getCancelButton</code>
     * will return <code>null</code>.
     * 
     * @return the cancel button or <code>null</code>
     * 
     * @see #createButton(Composite, int, String, boolean)
     * @since 2.0
     * @deprecated Use <code>getButton(IDialogConstants.CANCEL_ID)</code>
     *             instead. This method will be removed soon.
     */
    protected Button getCancelButton() {
        return getButton(IDialogConstants.CANCEL_ID);
    }
    /**
     * Returns the dialog area control.
     * <p>
     * Clients may call this framework method, but should not override it.
     * </p>
     * 
     * @return the dialog area, or <code>null</code> if the dialog area has
     *         not been created yet
     */
    protected Control getDialogArea() {
        return dialogArea;
    }
    /**
     * Returns the standard dialog image with the given key. Note that these