| /* |
| * 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 android.util.ArraySet; |
| import android.util.ExceptionUtils; |
| |
| import com.android.internal.util.FunctionalUtils.ThrowingConsumer; |
| |
| import java.util.ArrayList; |
| import java.util.Collection; |
| import java.util.Collections; |
| import java.util.List; |
| import java.util.Map; |
| import java.util.Set; |
| import java.util.function.Function; |
| import java.util.function.Predicate; |
| import java.util.stream.Stream; |
| |
| /** |
| * Utility methods for dealing with (typically {@code 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); |
| } |
| |
| /** |
| * @see #filter(List, java.util.function.Predicate) |
| */ |
| public static @NonNull <T> Set<T> filter(@Nullable Set<T> set, |
| java.util.function.Predicate<? super T> predicate) { |
| if (set == null || set.size() == 0) return Collections.emptySet(); |
| ArraySet<T> result = null; |
| if (set instanceof ArraySet) { |
| ArraySet<T> arraySet = (ArraySet<T>) set; |
| int size = arraySet.size(); |
| for (int i = 0; i < size; i++) { |
| final T item = arraySet.valueAt(i); |
| if (predicate.test(item)) { |
| result = ArrayUtils.add(result, item); |
| } |
| } |
| } else { |
| for (T item : set) { |
| if (predicate.test(item)) { |
| result = ArrayUtils.add(result, item); |
| } |
| } |
| } |
| return emptyIfNull(result); |
| } |
| |
| /** Add all elements matching {@code predicate} in {@code source} to {@code dest}. */ |
| public static <T> void addIf(@Nullable List<T> source, @NonNull Collection<? super T> dest, |
| @Nullable Predicate<? super T> predicate) { |
| for (int i = 0; i < size(source); i++) { |
| final T item = source.get(i); |
| if (predicate.test(item)) { |
| dest.add(item); |
| } |
| } |
| } |
| |
| /** |
| * 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 (isEmpty(cur)) 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; |
| } |
| |
| /** |
| * @see #map(List, Function) |
| */ |
| public static @NonNull <I, O> Set<O> map(@Nullable Set<I> cur, |
| Function<? super I, ? extends O> f) { |
| if (isEmpty(cur)) return Collections.emptySet(); |
| ArraySet<O> result = new ArraySet<>(); |
| if (cur instanceof ArraySet) { |
| ArraySet<I> arraySet = (ArraySet<I>) cur; |
| int size = arraySet.size(); |
| for (int i = 0; i < size; i++) { |
| result.add(f.apply(arraySet.valueAt(i))); |
| } |
| } else { |
| for (I item : cur) { |
| result.add(f.apply(item)); |
| } |
| } |
| return result; |
| } |
| |
| /** |
| * {@link #map(List, Function)} + {@link #filter(List, java.util.function.Predicate)} |
| * |
| * Calling this is equivalent (but more memory efficient) to: |
| * |
| * {@code |
| * filter( |
| * map(cur, f), |
| * i -> { i != null }) |
| * } |
| */ |
| public static @NonNull <I, O> List<O> mapNotNull(@Nullable List<I> cur, |
| Function<? super I, ? extends O> f) { |
| if (isEmpty(cur)) return Collections.emptyList(); |
| List<O> result = null; |
| for (int i = 0; i < cur.size(); i++) { |
| O transformed = f.apply(cur.get(i)); |
| if (transformed != null) { |
| result = add(result, transformed); |
| } |
| } |
| return emptyIfNull(result); |
| } |
| |
| /** |
| * Returns the given list, or an immutable empty list if the provided list is null |
| * |
| * This can be used to guarantee 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 given set, or an immutable empty set if the provided set is null |
| * |
| * This can be used to guarantee null-safety without paying the price of extra allocations |
| * |
| * @see Collections#emptySet |
| */ |
| public static @NonNull <T> Set<T> emptyIfNull(@Nullable Set<T> cur) { |
| return cur == null ? Collections.emptySet() : cur; |
| } |
| |
| /** |
| * Returns the size of the given collection, or 0 if null |
| */ |
| public static int size(@Nullable Collection<?> cur) { |
| return cur != null ? cur.size() : 0; |
| } |
| |
| /** |
| * Returns the size of the given map, or 0 if null |
| */ |
| public static int size(@Nullable Map<?, ?> cur) { |
| return cur != null ? cur.size() : 0; |
| } |
| |
| /** |
| * Returns whether the given collection {@link Collection#isEmpty is empty} or {@code null} |
| */ |
| public static boolean isEmpty(@Nullable Collection<?> cur) { |
| return size(cur) == 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 (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 (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; |
| } |
| |
| /** |
| * @see #add(List, Object) |
| */ |
| public static @NonNull <T> Set<T> add(@Nullable Set<T> cur, T val) { |
| if (cur == null || cur == Collections.emptySet()) { |
| cur = new ArraySet<>(); |
| } |
| 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 (isEmpty(cur)) { |
| return emptyIfNull(cur); |
| } |
| cur.remove(val); |
| return cur; |
| } |
| |
| /** |
| * @see #remove(List, Object) |
| */ |
| public static @NonNull <T> Set<T> remove(@Nullable Set<T> cur, T val) { |
| if (isEmpty(cur)) { |
| return emptyIfNull(cur); |
| } |
| cur.remove(val); |
| return cur; |
| } |
| |
| /** |
| * @return a list that will not be affected by mutations to the given original list. |
| */ |
| public static @NonNull <T> List<T> copyOf(@Nullable List<T> cur) { |
| return isEmpty(cur) ? Collections.emptyList() : new ArrayList<>(cur); |
| } |
| |
| /** |
| * @return a list that will not be affected by mutations to the given original list. |
| */ |
| public static @NonNull <T> Set<T> copyOf(@Nullable Set<T> cur) { |
| return isEmpty(cur) ? Collections.emptySet() : new ArraySet<>(cur); |
| } |
| |
| /** |
| * Applies {@code action} to each element in {@code cur} |
| * |
| * This avoids creating an iterator if the given set is an {@link ArraySet} |
| */ |
| public static <T> void forEach(@Nullable Set<T> cur, @Nullable ThrowingConsumer<T> action) { |
| if (cur == null || action == null) return; |
| int size = cur.size(); |
| if (size == 0) return; |
| try { |
| if (cur instanceof ArraySet) { |
| ArraySet<T> arraySet = (ArraySet<T>) cur; |
| for (int i = 0; i < size; i++) { |
| action.acceptOrThrow(arraySet.valueAt(i)); |
| } |
| } else { |
| for (T t : cur) { |
| action.acceptOrThrow(t); |
| } |
| } |
| } catch (Exception e) { |
| throw ExceptionUtils.propagate(e); |
| } |
| } |
| |
| public static @NonNull <T> List<T> defeatNullable(@Nullable List<T> val) { |
| return (val != null) ? val : Collections.emptyList(); |
| } |
| } |