Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
/*
 * Copyright 2015-2018 52North Initiative for Geospatial Open Source
 * Software GmbH
 *
 * 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.
 */

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;

import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;

import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Main {
    /**
     * @param collectionOfCollection
     *                               a {@code Collection<Collection<T>>}
     * @param <T>                    the element type
     *
     * @return a Set&lt;T&gt; containing all values of all Collections&lt;T&gt;
     *         without any duplicates
     */
    public static <T> Set<T> unionOfListOfLists(
            Collection<? extends Collection<? extends T>> collectionOfCollection) {
        return Optional.ofNullable(collectionOfCollection).map(Collection::stream).orElseGet(Stream::empty)
                .filter(Objects::nonNull).flatMap(c -> c.stream()).filter(Objects::nonNull)
                .collect(Collectors.toSet());
    }

    /**
     * @param entries
     *                the <i>final</i> set of entries to add to the newly created
     * <i>unmodifiable</i> map
     * @param <K>     the key type
     * @param <V>     the value type
     *
     * @return an <i>unmodifiable</i> map with all given entries
     */
    @SafeVarargs
    @SuppressWarnings("varargs")
    public static <K, V> Map<K, V> map(Entry<K, V>... entries) {
        return Collections
                .unmodifiableMap(Arrays.stream(entries).collect(Collectors.toMap(Entry::getKey, Entry::getValue)));
    }

    /**
     * @param <K> the key type
     * @param <V> the value type
     * @param m   the map
     *
     * @return an <b>UNMODIFIABLE</b> Map&lt;K, V&gt;
     */
    public static <K, V> Map<? extends K, ? extends V> unmodifiableMap(Map<? extends K, ? extends V> m) {
        return Optional.ofNullable(m).map(Collections::unmodifiableMap).orElseGet(Collections::emptyMap);
    }
}