Java 8 Convert a simple List to Map

Question

import java.util.function.*;
import java.util.*;
public class Main
{
    public static void main(String[] args) {
        List newList = new ArrayList<         


        

Answer 1

Your map step converts a Stream<Integer> to a Stream<Map<Integer,String>>. In order to collect that Stream to a single Map, you can write:

Map<Integer,String> newMap = 
    newList.stream()
           .flatMap(i->myFunc.apply(i).entrySet().stream())
           .collect(Collectors.toMap(Map.Entry::getKey, // keyMapper
                                     Map.Entry::getValue, // valueMapper
                                     (first, second) -> first,  // mergeFunction
                                     LinkedHashMap::new)); // mapFactory

or

Map<Integer,String> newMap = 
    newList.stream()
           .map(myFunc)
           .flatMap(m->m.entrySet().stream())
           .collect(Collectors.toMap(Map.Entry::getKey, // keyMapper
                                     Map.Entry::getValue, // valueMapper
                                     (first, second) -> first,  // mergeFunction
                                     LinkedHashMap::new)); // mapFactory

Of course, if all you want is to filter out the odd numbers and map the remaining numbers to "even", you can simply write:

Map<Integer,String> newMap = 
    newList.stream()
           .filter(i -> i % 2 == 0)
           .collect(Collectors.toMap(Function.identity(),
                                     i -> "even",
                                     (first, second) -> first,
                                     LinkedHashMap::new));