Java tutorial
/* * Copyright (c) 2015 Spotify AB. * * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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.spotify.heroic.common; import com.google.common.collect.ImmutableList; import com.google.common.collect.ImmutableSet; import com.google.common.collect.Iterables; import java.util.List; import java.util.Optional; import java.util.Set; import java.util.function.BinaryOperator; public final class Optionals { public static <T> Optional<List<T>> mergeOptionalList(final Optional<List<T>> a, Optional<List<T>> b) { return mergeOptional(a, b, (al, bl) -> ImmutableList.copyOf(Iterables.concat(al, bl))); } public static <T> Optional<Set<T>> mergeOptionalSet(final Optional<Set<T>> a, Optional<Set<T>> b) { return mergeOptional(a, b, (al, bl) -> ImmutableSet.copyOf(Iterables.concat(al, bl))); } public static <T> Optional<T> mergeOptional(Optional<T> a, Optional<T> b, BinaryOperator<T> merger) { if (a.isPresent() && b.isPresent()) { return Optional.of(merger.apply(a.get(), b.get())); } return pickOptional(a, b); } public static <T> Optional<T> pickOptional(Optional<T> a, Optional<T> b) { return b.isPresent() ? b : a; } public static <T> Optional<T> firstPresent(Optional<T> a, Optional<T> b) { return a.isPresent() ? a : b; } }