public static void main(String[] args) {
    // TODO Auto-generated method stub
    String v1 = "6.6.3.5.6";
    String v2 = "6.6.3.5a";

    long t1=System.currentTimeMillis();
    int result=compareVersionStr(v1, v2);
    System.out.println("time costs:"+(System.currentTimeMillis()-t1)+"  result:"+result);

}

public static int compareVersionStr(String v1, String v2) {
    if (v1 == null || v2 == null) {
        return COMPARE_VERSION_EXCEPTION;
    }
    v1 = v1.trim();
    v2 = v2.trim();
    boolean empty1 = v1.length() == 0;
    boolean empty2 = v2.length() == 0;
    if (!empty1 && empty2) {
        return COMPARE_VERSION_GREATER;
    }
    if (empty1 && !empty2) {
        return COMPARE_VERSION_SMALLER;
    }
    if (empty1 && empty2) {
        return COMPARE_VERSION_EQUAL;
    }

    if (!v1.contains(".")) {
        v1 = v1 + ".";
    }
    if (!v2.contains(".")) {
        v2 = v2 + ".";
    }
    int firstIndex1 = v1.indexOf(".");
    int firstIndex2 = v2.indexOf(".");
    System.out.println("firstIndex1:" + firstIndex1 + "   firstIndex2:"
            + firstIndex2);
    String firstVer1 = v1.substring(0, firstIndex1);
    String firstVer2 = v2.substring(0, firstIndex2);
    System.out.println("firstVer1:" + firstVer1 + "   firstVer2:"
            + firstVer2);

    int a = 0, b = 0;
    for (int i = 0; i < firstVer1.length(); i++) {
        a += firstVer1.charAt(i);
    }
    for (int i = 0; i < firstVer2.length(); i++) {
        b += firstVer2.charAt(i);
    }

    if (a > b) {
        return COMPARE_VERSION_GREATER;
    } else if (a < b) {
        return COMPARE_VERSION_SMALLER;
    } else {
        String subVer1 = v1.substring(firstIndex1 + 1, v1.length());
        String subVer2 = v2.substring(firstIndex2 + 1, v2.length());
        System.out.println("subVer1:" + subVer1 + "   subVer2:" + subVer2);
        return compareVersionStr(subVer1, subVer2);
    }
}