| // Copyright 2014 The Bazel Authors. All rights reserved. |
| // |
| // 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. |
| package com.google.devtools.build.lib.collect; |
| |
| import static com.google.common.collect.ImmutableSet.toImmutableSet; |
| |
| import com.google.common.collect.ImmutableSet; |
| import com.google.common.collect.Maps; |
| import com.google.devtools.build.lib.collect.compacthashset.CompactHashSet; |
| import java.util.Arrays; |
| import java.util.Collection; |
| import java.util.HashMap; |
| import java.util.HashSet; |
| import java.util.List; |
| import java.util.Map; |
| import java.util.Objects; |
| import java.util.Set; |
| import javax.annotation.Nullable; |
| |
| /** Utilities for collection classes. */ |
| public final class CollectionUtils { |
| |
| private CollectionUtils() {} |
| |
| /** Returns the set of all elements in the given list that appear more than once. */ |
| public static <T> Set<T> duplicatedElementsOf(List<T> input) { |
| int count = input.size(); |
| if (count < 2) { |
| return ImmutableSet.of(); |
| } |
| Set<T> duplicates = null; |
| Set<T> elementSet = CompactHashSet.createWithExpectedSize(count); |
| for (T el : input) { |
| if (!elementSet.add(el)) { |
| if (duplicates == null) { |
| duplicates = new HashSet<>(); |
| } |
| duplicates.add(el); |
| } |
| } |
| return duplicates == null ? ImmutableSet.of() : duplicates; |
| } |
| |
| /** |
| * Returns an immutable set of all non-null parameters in the order in which they are specified. |
| */ |
| public static <T> ImmutableSet<T> asSetWithoutNulls(T... elements) { |
| return Arrays.stream(elements).filter(Objects::nonNull).collect(toImmutableSet()); |
| } |
| |
| /** Returns a copy of the Map of Maps parameter. */ |
| public static <KEY_1, KEY_2, VALUE> Map<KEY_1, Map<KEY_2, VALUE>> copyOf( |
| Map<KEY_1, ? extends Map<KEY_2, VALUE>> map) { |
| return new HashMap<>(Maps.transformValues(map, HashMap::new)); |
| } |
| |
| /** |
| * Checks whether the given collection is either {@code null} or {@linkplain Collection#isEmpty |
| * empty}. |
| */ |
| public static boolean isNullOrEmpty(@Nullable Collection<?> collection) { |
| return collection == null || collection.isEmpty(); |
| } |
| } |