ca.uhn.fhir.util.CollectionUtil Maven / Gradle / Ivy
/*
* #%L
* HAPI FHIR - Core Library
* %%
* Copyright (C) 2014 - 2024 Smile CDR, Inc.
* %%
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* #L%
*/
package ca.uhn.fhir.util;
import jakarta.annotation.Nonnull;
import jakarta.annotation.Nullable;
import org.apache.commons.collections4.CollectionUtils;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import static java.util.Collections.unmodifiableCollection;
public class CollectionUtil {
/**
* Non instantiable
*/
private CollectionUtil() {
// nothing
}
/**
* Returns an immutable union of both collections. If either or both arguments are
* null they will be treated as an empty collection, meaning
* that even if both arguments are null, an empty immutable
* collection will be returned.
*
* DO NOT use this method if the underlying collections can be changed
* after calling this method, as the behaviour is indeterminate.
*
*
* @param theCollection0 The first set in the union, or null.
* @param theCollection1 The second set in the union, or null.
* @return Returns a union of both collections. Will not return null ever.
* @since 7.4.0
*/
@Nonnull
public static Collection nullSafeUnion(
@Nullable Collection theCollection0, @Nullable Collection theCollection1) {
Collection collection0 = theCollection0;
if (collection0 != null && collection0.isEmpty()) {
collection0 = null;
}
Collection collection1 = theCollection1;
if (collection1 != null && collection1.isEmpty()) {
collection1 = null;
}
if (collection0 == null && collection1 == null) {
return Collections.emptySet();
}
if (collection0 == null) {
return unmodifiableCollection(collection1);
}
if (collection1 == null) {
return unmodifiableCollection(collection0);
}
return CollectionUtils.union(collection0, collection1);
}
/**
* This method is equivalent to Set.of(...) but is kept here
* and used instead of that method because Set.of is not present on Android
* SDKs (at least up to 29).
*
* Sets returned by this method are unmodifiable.
*
*/
@SuppressWarnings("unchecked")
public static Set newSet(T... theValues) {
HashSet retVal = new HashSet<>();
Collections.addAll(retVal, theValues);
return Collections.unmodifiableSet(retVal);
}
}