Made this for a colleague. An arguably, improved way to use streams api to parse a collection, providing the index (for failure messages)

ListToIndexedMapBuilder.java

package org.outrospective.streams;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ConcurrentMap;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class ListToIndexedMapBuilder {

    public static void main(String[] args) {
        new ListToIndexedMapBuilder();

    }

    public ListToIndexedMapBuilder() {
        List<String> originalCollection = Arrays.asList("foo", "bar", "scar", "mars", "bars", "bar");

        ConcurrentMap<Integer, String> indexedList = indexedList(originalCollection);

        System.out.println("indexedList = " + indexedList);
    }

    public static ConcurrentMap<Integer, String> indexedList(List<String> list) {
        return IntStream.range(0, list.size())
                // the next two lines aren't req'd but:
                .parallel()  // I was curious if for a large enough list parallel would be better
                .unordered() // Making the stream unordered would allow for better parallelisation potentially
                .boxed()
                .collect(Collectors.toConcurrentMap( // toMap could have been ok here too
                    Function.identity(),
                    list::get));
    }

}