### Question:
TupleDomain { public <U> TupleDomain<U> transform(Function<T, U> function) { if (isNone()) { return none(); } if (isAll()) { return all(); } Map<T, Domain> domains = this.domains.orElseThrow(); HashMap<U, Domain> result = new LinkedHashMap<>(domains.size()); for (Map.Entry<T, Domain> entry : domains.entrySet()) { U key = function.apply(entry.getKey()); if (key == null) { continue; } Domain previous = result.put(key, entry.getValue()); if (previous != null) { throw new IllegalArgumentException(format("Every argument must have a unique mapping. %s maps to %s and %s", entry.getKey(), entry.getValue(), previous)); } } return TupleDomain.withColumnDomains(result); } private  TupleDomain(Optional<Map<T, Domain>> domains); static TupleDomain<T> withColumnDomains(Map<T, Domain> domains); @SuppressWarnings("unchecked") static TupleDomain<T> none(); @SuppressWarnings("unchecked") static TupleDomain<T> all(); static Optional<Map<T, NullableValue>> extractFixedValues(TupleDomain<T> tupleDomain); static Optional<Map<T, List<NullableValue>>> extractDiscreteValues(TupleDomain<T> tupleDomain); static TupleDomain<T> fromFixedValues(Map<T, NullableValue> fixedValues); @JsonCreator // Available for Jackson deserialization only! static TupleDomain<T> fromColumnDomains(@JsonProperty("columnDomains") Optional<List<ColumnDomain<T>>> columnDomains); @JsonProperty // Available for Jackson serialization only! Optional<List<ColumnDomain<T>>> getColumnDomains(); boolean isAll(); boolean isNone(); @JsonIgnore Optional<Map<T, Domain>> getDomains(); TupleDomain<T> intersect(TupleDomain<T> other); @SafeVarargs static TupleDomain<T> columnWiseUnion(TupleDomain<T> first, TupleDomain<T> second, TupleDomain<T>... rest); static TupleDomain<T> columnWiseUnion(List<TupleDomain<T>> tupleDomains); boolean overlaps(TupleDomain<T> other); boolean contains(TupleDomain<T> other); @Override boolean equals(Object obj); @Override int hashCode(); @Override String toString(); String toString(ConnectorSession session); TupleDomain<T> filter(BiPredicate<T, Domain> predicate); TupleDomain<U> transform(Function<T, U> function); TupleDomain<T> simplify(); TupleDomain<T> simplify(int threshold); TupleDomain<T> transformDomains(BiFunction<T, Domain, Domain> transformation);  }### Answer:
@Test public void testTransform() { Map<Integer, Domain> domains = ImmutableMap.<Integer, Domain>builder() .put(1, Domain.singleValue(BIGINT, 1L)) .put(2, Domain.singleValue(BIGINT, 2L)) .put(3, Domain.singleValue(BIGINT, 3L)) .build(); TupleDomain<Integer> domain = TupleDomain.withColumnDomains(domains); TupleDomain<String> transformed = domain.transform(Object::toString); Map<String, Domain> expected = ImmutableMap.<String, Domain>builder() .put("1", Domain.singleValue(BIGINT, 1L)) .put("2", Domain.singleValue(BIGINT, 2L)) .put("3", Domain.singleValue(BIGINT, 3L)) .build(); assertEquals(transformed.getDomains().get(), expected); }