Casting an Object to List

Question

I have a Map<String,Object> which contains an element value of List<String>

Now I need to filter the latter and retrieve first value that contains @.

The best I did was:

    Map<String, Object> map = new HashMap<>();
    map.put("alias", List.of("Mxxx", "fstarred@mymail.org"));

    final Object obj = map.get("alias");
    final List lst = (List) obj;
    final Object output= lst.stream()
            .filter(o -> ((String) o).contains("@"))
            .findFirst()
            .orElse(null);

however looks to much verbose and mostly requires:

a final cast to String of output
a cast for each object passed into filter

For the above issued, I tried .map(String.class::cast)

After lst.stream()
After filter(o -> ((String) o).contains("@"))

None of these approaches did work.

Any hints?

[Never use raw types](https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it) like `List`, as it messes everything up. Cast to `List` (which won't actually verify anything, it's an unchecked cast, but it will make your life easier). — Joachim Sauer, Sep 02 '20 at 12:33

score 5 · Accepted Answer · answered Sep 02 '20 at 12:43

As suggested, don't use raw types. Here is the approach you should use.

Map<String, List<String>> map = new HashMap<>();
map.put("alias", List.of("Mxxx", "fstarred@mymail.org"));

List<String> list = map.get("alias");

String output= list.stream()
         .filter(o ->o.contains("@"))
         .findFirst()
         .orElse(null);

System.out.println(output);

Prints

fstarred@mymail.org

Casting an Object to List

1 Answers1