Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
/**
 * Copyright 2013-present febit.org (support@febit.org)
 *
 * 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.*;
import java.util.function.Function;

public class Main {
    public static <T, K> TreeMap<K, List<T>> groupToTreeMap(Collection<T> collection, Function<T, K> keyFunc) {
        return groupToTreeMap(collection, keyFunc, (T arg1) -> arg1);
    }

    public static <T, K, V> TreeMap<K, List<V>> groupToTreeMap(Collection<T> collection, Function<T, K> keyFunc,
            Function<T, V> valueFunc) {
        TreeMap<K, List<V>> map = new TreeMap<>();
        groupToMap(map, collection, keyFunc, valueFunc);
        return map;
    }

    public static <T, K> Map<K, List<T>> groupToMap(Collection<T> collection, Function<T, K> keyFunc) {
        return groupToMap(collection, keyFunc, (T arg1) -> arg1);
    }

    public static <T, K, V> Map<K, List<V>> groupToMap(Collection<T> collection, Function<T, K> keyFunc,
            Function<T, V> valueFunc) {
        Map<K, List<V>> map = new HashMap<>();
        groupToMap(map, collection, keyFunc, valueFunc);
        return map;
    }

    protected static <T, K, V> void groupToMap(Map<K, List<V>> map, Collection<T> collection,
            Function<T, K> keyFunc, Function<T, V> valueFunc) {
        for (T t : collection) {
            K key = keyFunc.apply(t);
            List<V> list = map.computeIfAbsent(key, k -> new ArrayList<>());
            list.add(valueFunc.apply(t));
        }
    }
}