implement frequency and unique? in java8

java8 - frequency and unique?

// frequency
Stream.of("a", "a", "b", "c").collect(toMap(identity(), a -> 1, (a, b) -> a + b));
Stream.of("a", "a", "b", "c").collect(groupingBy(identity(), counting()));
Stream.of("a", "a", "b", "c").collect(groupingBy(identity(), summingInt(v -> 1)));
Stream.of("a", "a", "b", "c").collect(groupingBy(identity(), mapping(identity(), summingInt(v -> 1))));
-> {a=2, b=1, c=1}

// unique?
frequency().values().stream().anyMatch(c -> c > 1);