What does this statement mean in java jdk 1.8 ( java.util.Map)

Question

There is a statement in the code shown below that I can't understand its meaning.I hope someone can explain it to me. I cannot find the answer with Google.T_T

public static <K, V extends Comparable<? super V>> Comparator<Map.Entry<K,V>> comparingByValue() {
            return (Comparator<Map.Entry<K, V>> & Serializable)
                (c1, c2) -> c1.getValue().compareTo(c2.getValue());
}

look at this statement Comparator<Map.Entry<K, V>> & Serializable

I am confused about & appearing here.