Java 8 List into Map where K is a new object that needs V in its constructor

Question

Before Java 8 I would code it like this:

Map<String, K> resultMap = new HashMap<>();
for (str : stringsList) {
    resultMap.put(str, new K(str, new X(), new Y());
}

Is there any way for me to do it Java 8 style instead?

Answer 1

In theory, you can write:

Map<String, K> resultMap =
  stringsList.stream().collect(Collectors.toMap(
    str ->   /*key=*/ str,
    str -> /*value=*/ new K(str, new X(), new Y())
  ));

(using java.util.stream.Collectors.toMap(Function, Function)).

In practice, I think your current code is probably clearer.

Answer 2

solving duplicate key collisions from ruakh's answer:

Map<String, K> resultMap = stringsList.stream()
    .collect(Collectors.toMap(
        str -> str, 
        str -> new K(str, new X(), new Y()), 
        (oldVal, newVal) -> newVal)
);

Answer 3

Java 8 Interable Foreach:

List<String> stringsList = Arrays.asList("123", "456", "789");
Map<String, K> resultMap = new HashMap<String, K>();
stringsList.forEach(item -> resultMap.put(item, new K(item, new X(), new Y())));