@Override
    public String toString() {
        if (str == null)
            str = toStringBuilder().toString();
        return str;
    }
@Test
    public void testToString() {
        ItemPointer ip = new ItemPointer(Tag.RequestAttributesSequence);
        AttributeSelector selector = new AttributeSelector(Tag.StudyInstanceUID, null, ip);
        assertEquals(XPATH, selector.toString());
    }