com.cinchapi.impromptu.server.util.MappedCollections Maven / Gradle / Ivy

Go to download
/*
 * Copyright (c) 2013-2017 Cinchapi Inc.
 * 
 * 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.cinchapi.impromptu.server.util;

import java.util.Collection;
import java.util.Iterator;
import java.util.Map;

/**
 * Utility functions for {@link Map Maps} that contain {@link Collection
 * Collections} for values.
 * 
 * @author Jeff Nelson
 */
public final class MappedCollections {

    /**
     * Return the first item in the {@link Collection} mapped from the
     * {@code key} within the {@code data}.
     * 
     * @param data the dataset
     * @param key the lookup key
     * @return the first item in the collection mapped from the {@code key} or
     *         {@code null} if there is no mapping from {@code key}.
     */
    public static  V getFirst(Map> data, K key) {
        Collection values = data.get(key);
        if(values == null || values.isEmpty()) {
            return null;
        }
        else {
            return getIterableFirstOrDefault(values, null);
        }
    }

    /**
     * Return the first item in the {@link Collection} mapped from the
     * {@code key} within the {@code data} or {@code theDefault} value if no
     * mapping from {@code key} exists.
     * 
     * @param data the dataset
     * @param key the lookup key
     * @return the first item in the collection mapped from the {@code key} or
     *         {@code theDefault} if there is no mapping from {@code key}.
     */
    public static  V getFirstOrDefault(Map> data, K key,
            V theDefault) {
        Collection values = data.get(key);
        if(values == null || values.isEmpty()) {
            return theDefault;
        }
        else {
            return getIterableFirstOrDefault(values, theDefault);
        }
    }

    /**
     * Return the first item in the {@code iterable} or {@code theDefault} if
     * the {@code iterable} is empty.
     * 
     * @param iterable the iterable from which the first item is returned
     * @param theDefault the default value to return if the iterable is empty
     * @return the first or default item
     */
    private static  T getIterableFirstOrDefault(Iterable iterable,
            T theDefault) {
        Iterator it = iterable.iterator();
        if(it.hasNext()) {
            return it.next();
        }
        else {
            return theDefault;
        }
    }

    private MappedCollections() {/* no-op */}

}