is palindrome permutation with bit vector

gistfile1.java

    public static boolean isPalindromePerm(String s) {
        int checker = 0;
        for (char c : s.toCharArray()) {
            if ('a' <= c && c <= 'z') {
                int val = c - 'a';
                int mask = 1 << val;
                if ((checker & mask) == 0) {
                    checker |= mask; //flip to 1
                } else {
                    checker &= ~mask; //flip to 0
                }
            }
        }
        return checker == 0 || ((checker & (checker - 1)) == 0);//either even or odd
    }