/** * Compare * * @param o1 object 1 * @param o2 object 2 * @return -1,0, 1 */ @Override public int compare(PO o1, PO o2) { String s1 = o1.toString(); if (s1 == null) s1 = ""; String s2 = o2.toString(); if (s2 == null) s2 = ""; return s1.compareTo(s2); } // compare