public int compare(String s1,
    String s2) 
{
        int n1=s1.length(), n2=s2.length();
        int minLen = n1 <  n2 ? n1 : n2;
        for (int i=0; i <  minLen; i++) {
            char c1 = s1.charAt(i);
            char c2 = s2.charAt(i);
            assert c1 < = '\u007F' && c2 < = '\u007F';
            if (c1 != c2) {
                c1 = (char)toLower(c1);
                c2 = (char)toLower(c2);
                if (c1 != c2) {
                    return c1 - c2;
                }
            }
        }
        return n1 - n2;
}

 static boolean isLower(int ch) 
{
        return ((ch-'a')|('z'-ch))  >= 0;
}

 static boolean isUpper(int ch) 
{
        return ((ch-'A')|('Z'-ch))  >= 0;
}

 public static int lowerCaseHashCode(String s) 
{
        int h = 0;
        int len = s.length();
        for (int i = 0; i <  len; i++) {
            h = 31*h + toLower(s.charAt(i));
        }
        return h;
}

A case insensitive hash code method to go with the case insensitive compare() method. Returns a hash code for this ASCII string as if it were lower case. returns same answer as:

s.toLowerCase(Locale.US).hashCode();

but does not allocate memory (it does NOT have the special case Turkish rules).

 static int toLower(int ch) 
{
        return isUpper(ch) ? (ch + 0x20) : ch;
}

 static int toUpper(int ch) 
{
        return isLower(ch) ? (ch - 0x20) : ch;
}