Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
//License from project: Open Source License 

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;

import java.util.Map;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collectors;

public class Main {

    public static <T, K> ArrayList<T> buildTree(Collection<T> list, Function<T, K> keyMapper,
            Function<T, K> parentKeyMapper, Function<T, Collection<T>> childMapper) {
        HashMap<K, T> map = toHashMap(list, keyMapper);

        ArrayList<T> root = new ArrayList<T>();
        for (T t : list) {
            K key = keyMapper.apply(t);
            K parentKey = parentKeyMapper.apply(t);
            if (parentKey == null || key.equals(parentKey))
                root.add(t);
            else
                childMapper.apply(map.get(parentKey)).add(t);
        }

        return root;
    }

    /**
     * Convert a collection to HashMap, The key is decided by keyMapper, value
     * is the object in collection
     * 
     * @param entities
     * @param keyMapper
     * @return
     */

    public static <T, K> HashMap<K, T> toHashMap(Collection<T> entities, Function<T, K> keyMapper) {
        return toMap(entities, keyMapper, HashMap<K, T>::new);
    }

    public static <T, K> HashMap<K, T> toHashMap(T[] entities, Function<T, K> keyMapper) {
        return toHashMap(Arrays.asList(entities), keyMapper);
    }

    public static <T, K, V> HashMap<K, V> toHashMap(Collection<T> entities, Function<T, K> keyMapper,
            Function<T, V> valueMapper) {
        return toMap(entities, keyMapper, valueMapper, HashMap<K, V>::new);
    }

    public static <T, K, V> HashMap<K, V> toHashMap(T[] entities, Function<T, K> keyMapper,
            Function<T, V> valueMapper) {
        return toHashMap(Arrays.asList(entities), keyMapper, valueMapper);
    }

    public static <T, K, M extends Map<K, T>> M toMap(Collection<T> entities, Function<T, K> keyMapper,
            Supplier<M> supplier) {
        return entities.stream().collect(Collectors.toMap(keyMapper, Function.identity(), (a, b) -> b, supplier));
    }

    public static <T, K, V, M extends Map<K, V>> M toMap(Collection<T> entities, Function<T, K> keyMapper,
            Function<T, V> valueMapper, Supplier<M> supplier) {
        return entities.stream().collect(Collectors.toMap(keyMapper, valueMapper, (a, b) -> b, supplier));
    }
}