| /* |
| * Copyright (C) 2017 The Android Open Source Project |
| * |
| * 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.android.internal.util; |
| |
| import android.annotation.NonNull; |
| import android.annotation.Nullable; |
| |
| import java.util.ArrayList; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.List; |
| import java.util.function.Function; |
| import java.util.stream.Stream; |
| |
| /** |
| * Utility methods for dealing with (typically {@link Nullable}) {@link Collection}s |
| * |
| * Unless a method specifies otherwise, a null value for a collection is treated as an empty |
| * collection of that type. |
| */ |
| public class CollectionUtils { |
| private CollectionUtils() { /* cannot be instantiated */ } |
| |
| /** |
| * Returns a list of items from the provided list that match the given condition. |
| * |
| * This is similar to {@link Stream#filter} but without the overhead of creating an intermediate |
| * {@link Stream} instance |
| */ |
| public static @NonNull <T> List<T> filter(@Nullable List<T> list, |
| java.util.function.Predicate<? super T> predicate) { |
| ArrayList<T> result = null; |
| for (int i = 0; i < size(list); i++) { |
| final T item = list.get(i); |
| if (predicate.test(item)) { |
| result = ArrayUtils.add(result, item); |
| } |
| } |
| return emptyIfNull(result); |
| } |
| |
| /** |
| * Returns a list of items resulting from applying the given function to each element of the |
| * provided list. |
| * |
| * The resulting list will have the same {@link #size} as the input one. |
| * |
| * This is similar to {@link Stream#map} but without the overhead of creating an intermediate |
| * {@link Stream} instance |
| */ |
| public static @NonNull <I, O> List<O> map(@Nullable List<I> cur, |
| Function<? super I, ? extends O> f) { |
| if (cur == null || cur.isEmpty()) return Collections.emptyList(); |
| final ArrayList<O> result = new ArrayList<>(); |
| for (int i = 0; i < cur.size(); i++) { |
| result.add(f.apply(cur.get(i))); |
| } |
| return result; |
| } |
| |
| /** |
| * Returns the given list, or an immutable empty list if the provided list is null |
| * |
| * This can be used to guaranty null-safety without paying the price of extra allocations |
| * |
| * @see Collections#emptyList |
| */ |
| public static @NonNull <T> List<T> emptyIfNull(@Nullable List<T> cur) { |
| return cur == null ? Collections.emptyList() : cur; |
| } |
| |
| /** |
| * Returns the size of the given list, or 0 if the list is null |
| */ |
| public static int size(@Nullable Collection<?> cur) { |
| return cur != null ? cur.size() : 0; |
| } |
| |
| /** |
| * Returns the elements of the given list that are of type {@code c} |
| */ |
| public static @NonNull <T> List<T> filter(@Nullable List<?> list, Class<T> c) { |
| if (ArrayUtils.isEmpty(list)) return Collections.emptyList(); |
| ArrayList<T> result = null; |
| for (int i = 0; i < list.size(); i++) { |
| final Object item = list.get(i); |
| if (c.isInstance(item)) { |
| result = ArrayUtils.add(result, (T) item); |
| } |
| } |
| return emptyIfNull(result); |
| } |
| |
| /** |
| * Returns whether there exists at least one element in the list for which |
| * condition {@code predicate} is true |
| */ |
| public static <T> boolean any(@Nullable List<T> items, |
| java.util.function.Predicate<T> predicate) { |
| return find(items, predicate) != null; |
| } |
| |
| /** |
| * Returns the first element from the list for which |
| * condition {@code predicate} is true, or null if there is no such element |
| */ |
| public static @Nullable <T> T find(@Nullable List<T> items, |
| java.util.function.Predicate<T> predicate) { |
| if (ArrayUtils.isEmpty(items)) return null; |
| for (int i = 0; i < items.size(); i++) { |
| final T item = items.get(i); |
| if (predicate.test(item)) return item; |
| } |
| return null; |
| } |
| |
| /** |
| * Similar to {@link List#add}, but with support for list values of {@code null} and |
| * {@link Collections#emptyList} |
| */ |
| public static @NonNull <T> List<T> add(@Nullable List<T> cur, T val) { |
| if (cur == null || cur == Collections.emptyList()) { |
| cur = new ArrayList<>(); |
| } |
| cur.add(val); |
| return cur; |
| } |
| |
| /** |
| * Similar to {@link List#remove}, but with support for list values of {@code null} and |
| * {@link Collections#emptyList} |
| */ |
| public static @NonNull <T> List<T> remove(@Nullable List<T> cur, T val) { |
| if (cur == null || cur == Collections.emptyList()) { |
| return Collections.emptyList(); |
| } |
| cur.remove(val); |
| return cur; |
| } |
| |
| } |