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
};
    /**
     * Creates a dialog instance. Note that the window will have no visual
     * representation (no widgets) until it is told to open. By default,
     * <code>open</code> blocks for dialogs.
     * 
     * @param parentShell
     *            the parent shell, or <code>null</code> to create a top-level
     *            shell
     */
    protected Dialog(Shell parentShell) {
        this(new SameShellProvider(parentShell));
        if (parentShell == null && Policy.DEBUG_DIALOG_NO_PARENT)
            Policy.getLog().log(
                    new Status(IStatus.INFO, Policy.JFACE, IStatus.INFO, this
                            .getClass()
                            + " created with no shell",
                            new Exception()));
    }
    
    /**
     * Creates a dialog with the given parent. 
     * 
     * @param parentShell object that returns the current parent shell
     * 
     * @since 3.1
     */
    protected Dialog(IShellProvider parentShell) {
        super(parentShell);
        setShellStyle(SWT.DIALOG_TRIM | SWT.APPLICATION_MODAL | getDefaultOrientation());