what is the explain to the solution of the qustion Implement an algorithm to determine if a string has all unique characters? : I don't understand the solution
Can I get explain of that:

    public static boolean isUniqueChars(String str) {
    int checker = 0;
    for (int i = 0; i < str.length(); ++i) {
    int val = str.charAt(i) - ‘a’;
    if ((checker & (1 << val)) > 0) return false;
    checker |= (1 << val);
    }
    return true;
    }