@Override
    public <VR> KTable<K, VR> mapValues(final ValueMapper<? super V, ? extends VR> mapper,
                                        final Named named) {
        Objects.requireNonNull(mapper, "mapper can't be null");
        return doMapValues(withKey(mapper), named, null);
    }
The implementation class of {@link KTable}.

@param <K> the key type
@param <S> the source's (parent's) value type
@param <V> the value type
streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableImpl.java