public class Hamming {

    Hamming(String leftStrand, String rightStrand) {
        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
    }

    int getHammingDistance() {
        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
    }

}

class Hamming {

    Hamming(String leftStrand, String rightStrand) {
        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
    }

    int getHammingDistance() {
        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
    }

}

change class to package private.