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
setBlockOnOpen(true);        
    }
    /**
     * Notifies that this dialog's button with the given id has been pressed.
     * <p>
     * The <code>Dialog</code> implementation of this framework method calls
     * <code>okPressed</code> if the ok button is the pressed, and
     * <code>cancelPressed</code> if the cancel button is the pressed. All
     * other button presses are ignored. Subclasses may override to handle other
     * buttons, but should call <code>super.buttonPressed</code> if the
     * default handling of the ok and cancel buttons is desired.
     * </p>
     * @param buttonId
     *            the id of the button that was pressed (see
     *            <code>IDialogConstants.*_ID</code> constants)
     */
    protected void buttonPressed(int buttonId) {
        if (IDialogConstants.OK_ID == buttonId)
            okPressed();
        else if (IDialogConstants.CANCEL_ID == buttonId)
            cancelPressed();
    }
    /**
     * Notifies that the cancel button of this dialog has been pressed.
     * <p>
     * The <code>Dialog</code> implementation of this framework method sets
     * this dialog's return code to <code>Window.CANCEL</code> and closes the
     * dialog. Subclasses may override if desired.
     * </p>
     */