+
+ /**
+ * Check whether specified Map is {@code null} and if so return an immutable map instead. This method supports
+ * non-null default getter methods.
+ *
+ * @param <K> key type
+ * @param <V> value type
+ * @param input input map, may be {@code null}
+ * @return Input map or an empty map.
+ */
+ public static <K, V> @NonNull Map<K, V> nonnull(final @Nullable Map<K, V> input) {
+ return input != null ? input : ImmutableMap.of();
+ }
+
+ /**
+ * Check whether specified List is empty and if so return {@code null}, otherwise return input list. This method
+ * supports Builder/implementation list handover.
+ *
+ * @param <T> list element type
+ * @param input input list, may be {@code null}
+ * @return Input list or {@code null}.
+ */
+ public static <T> @Nullable List<T> emptyToNull(final @Nullable List<T> input) {
+ return input != null && input.isEmpty() ? null : input;
+ }
+
+ /**
+ * Check whether specified Map is empty and if so return {@code null}, otherwise return input map. This method
+ * supports Builder/implementation list handover.
+ *
+ * @param <K> key type
+ * @param <V> value type
+ * @param input input map, may be {@code null}
+ * @return Input map or {@code null}.
+ */
+ public static <K, V> @Nullable Map<K, V> emptyToNull(final @Nullable Map<K, V> input) {
+ return input != null && input.isEmpty() ? null : input;
+ }
+
+ /**
+ * Return hash code of a single-property wrapper class. Since the wrapper is not {@code null}, we really want to
+ * discern this object being present, hence {@link Objects#hashCode()} is not really useful we would end up with
+ * {@code 0} for both non-present and present-with-null objects.
+ *
+ * @param obj Internal object to hash
+ * @return Wrapper object hash code
+ */
+ public static int wrapperHashCode(final @Nullable Object obj) {
+ return wrapHashCode(Objects.hashCode(obj));
+ }
+
+ /**
+ * Return hash code of a single-property wrapper class. Since the wrapper is not {@code null}, we really want to
+ * discern this object being present, hence {@link Arrays#hashCode()} is not really useful we would end up with
+ * {@code 0} for both non-present and present-with-null objects.
+ *
+ * @param obj Internal object to hash
+ * @return Wrapper object hash code
+ */
+ public static int wrapperHashCode(final byte @Nullable[] obj) {
+ return wrapHashCode(Arrays.hashCode(obj));
+ }
+
+ /**
+ * The constant '31' is the result of folding this code:
+ * <pre>
+ * <code>
+ * final int prime = 31;
+ * int result = 1;
+ * result = result * prime + Objects.hashCode(obj);
+ * return result;
+ * </code>
+ * </pre>
+ * when hashCode is returned as 0, such as due to obj being {@code null} or its hashCode being 0.
+ *
+ * @param hash Wrapped object hash
+ * @return Wrapper object hash
+ */
+ private static int wrapHashCode(final int hash) {
+ return hash == 0 ? 31 : hash;
+ }
+
+ /**
+ * Check that the specified {@link EnumTypeObject} object is not {@code null}. This method is meant to be used with
+ * {@code ofName(String)} and {@code ofValue(int)} static factory methods.
+ *
+ * @param obj enumeration object, possibly {@code null}
+ * @param name User-supplied enumeration name
+ * @return Enumeration object
+ * @throws IllegalArgumentException if {@code obj} is {@code null}
+ */
+ public static <T extends EnumTypeObject> @NonNull T checkEnum(final @Nullable T obj, final String name) {
+ if (obj == null) {
+ throw new IllegalArgumentException("\"" + name + "\" is not a valid name");
+ }
+ return obj;
+ }
+
+ /**
+ * Check that the specified {@link EnumTypeObject} object is not {@code null}. This method is meant to be used with
+ * {@code ofName(String)} and {@code ofValue(int)} static factory methods.
+ *
+ * @param obj enumeration object, possibly {@code null}
+ * @param value User-supplied enumeration value
+ * @return Enumeration object
+ * @throws IllegalArgumentException if {@code obj} is {@code null}
+ */
+ public static <T extends EnumTypeObject> @NonNull T checkEnum(final @Nullable T obj, final int value) {
+ if (obj == null) {
+ throw new IllegalArgumentException(value + " is not a valid value");
+ }
+ return obj;
+ }
+
+ /**
+ * Utility method for checking whether a target object is a compatible {@link BindingContract}.
+ *
+ * @param requiredClass Required BindingContract class
+ * @param obj Object to check, may be {@code null}
+ * @return Object cast to required class, if its implemented class matches requirement, {@code null} otherwise
+ * @throws NullPointerException if {@code requiredClass} is {@code null}
+ */
+ public static <T extends BindingContract<?>> @Nullable T checkCast(final @NonNull Class<T> requiredClass,
+ final @Nullable Object obj) {
+ return obj instanceof BindingContract<?> contract && requiredClass.equals(contract.implementedInterface())
+ ? requiredClass.cast(obj) : null;
+ }
+
+ /**
+ * Utility method for checking whether a target object is compatible.
+ *
+ * @param requiredClass Required class
+ * @param fieldName name of the field being filled
+ * @param obj Object to check, may be {@code null}
+ * @return Object cast to required class, if its class matches requirement, or {@code null}
+ * @throws IllegalArgumentException if {@code obj} is not an instance of {@code requiredClass}
+ * @throws NullPointerException if {@code requiredClass} or {@code fieldName} is {@code null}
+ */
+ public static <T> @Nullable T checkFieldCast(final @NonNull Class<T> requiredClass, final @NonNull String fieldName,
+ final @Nullable Object obj) {
+ try {
+ return requiredClass.cast(obj);
+ } catch (ClassCastException e) {
+ throw new IllegalArgumentException("Invalid input value for property \"" + fieldName + "\"", e);
+ }
+ }
+
+ /**
+ * Utility method for checking whether the items of target list is compatible.
+ *
+ * @param requiredClass Required item class
+ * @param fieldName name of the field being filled
+ * @param list List, which items should be checked
+ * @return Type-checked List
+ * @throws IllegalArgumentException if a list item is not instance of {@code requiredClass}
+ * @throws NullPointerException if {@code requiredClass} or {@code fieldName} is {@code null}
+ */
+ @SuppressWarnings("unchecked")
+ public static <T> @Nullable List<T> checkListFieldCast(final @NonNull Class<?> requiredClass,
+ final @NonNull String fieldName, final @Nullable List<?> list) {
+ DoNotLeakSpotbugs.checkCollectionField(requiredClass, fieldName, list);
+ return (List<T>) list;
+ }
+
+ /**
+ * Utility method for checking whether the items of target set is compatible.
+ *
+ * @param requiredClass Required item class
+ * @param fieldName name of the field being filled
+ * @param set Set, which items should be checked
+ * @return Type-checked Set
+ * @throws IllegalArgumentException if a set item is not instance of {@code requiredItemClass}
+ * @throws NullPointerException if {@code requiredClass} or {@code fieldName} is {@code null}
+ */
+ @SuppressWarnings("unchecked")
+ public static <T> @Nullable Set<T> checkSetFieldCast(final @NonNull Class<?> requiredClass,
+ final @NonNull String fieldName, final @Nullable Set<?> set) {
+ DoNotLeakSpotbugs.checkCollectionField(requiredClass, fieldName, set);
+ return (Set<T>) set;
+ }