ImmutableMapFactory { public static <K, V> ImmutableMap<K, V> filter( Map<K, V> baseMap, BiPredicate<K, V> filter) { return baseMap.entrySet().stream() .filter(e -> filter.test(e.getKey(), e.getValue())) .collect(ImmutableMap.toImmutableMap( Entry::getKey, Entry::getValue)); }  static ImmutableMap<L, W> create(
            Map<K, V> baseMap,
            BiFunction<? super K, ? super V, ? extends L> keyCreator,
            BiFunction<? super K, ? super V, ? extends W> valueCreator); static ImmutableMap<L, W> create(
            Map<K, V> baseMap,
            Function<? super K, ? extends L> keyMapper,
            Function<? super V, ? extends W> valueMapper); static ImmutableMap<L, W> createAndReduceCollisions(
            Map<K, V> baseMap,
            Function<? super K, ? extends L> keyMapper,
            Function<? super V, ? extends W> valueMapper,
            W valueIdentity,
            BinaryOperator<W> collidingKeysAccumulator); static ImmutableMap<L, V> createWithNewKeys(
            Map<K, V> baseMap,
            Function<? super K, ? extends L> keyMapper); static ImmutableMap<K, W> createWithNewValues(
            Map<K, V> baseMap,
            Function<? super V, ? extends W> valueMapper); static ImmutableMap<K, W> createWithNewValues(
            Map<K, V> baseMap,
            BiFunction<? super K, ? super V, ? extends W> valueMapper); static ImmutableMap<K, V> createFromKeys(
            Collection<K> keys,
            Supplier<V> valueSupplier); static ImmutableMap<K, V> createFromKeys(
            Collection<K> keys,
            Function<K, V> valueCreator); static ImmutableMap<K, V> zip(
            List<K> keys,
            List<V> values); static ImmutableMap<K, V> filter(
            Map<K, V> baseMap,
            BiPredicate<K, V> filter); static ImmutableMap<K, V> filterByKeys(
            Map<K, V> baseMap,
            Predicate<K> keyFilter); static ImmutableMap<K, V> filterByValues(
            Map<K, V> baseMap,
            Predicate<V> valueFilter); static ImmutableMap<K, V> parse(
            String s,
            Function<String, K> keyParser,
            Function<String, V> valueParser); static ImmutableMap<K, V> parseAndFilter(
            String s,
            Function<String, K> keyParser,
            Function<String, V> valueParser,
            BiPredicate<K, V> filter);  }
@Test void testFilter() { ImmutableMap<String, Integer> toFilter = ImmutableMap.of( "A", 1, "B", 2, "C", 3, "D", 4); ImmutableMap<String, Integer> expected = ImmutableMap.of( "B", 2, "C", 3); ImmutableMap<String, Integer> actual = ImmutableMapFactory.filter(toFilter, (key, value) -> value < 4 && !key.equals("A")); Assertions.assertEquals(expected, actual); }
@Test void testFilterNoneRemain() { ImmutableMap<String, Integer> toFilter = ImmutableMap.of( "A", 1, "B", 2, "C", 3, "D", 4); ImmutableMap<String, Integer> expected = ImmutableMap.of(); ImmutableMap<String, Integer> actual = ImmutableMapFactory.filter(toFilter, (key, value) -> value > 50 && !key.equals("A")); Assertions.assertEquals(expected, actual); }