Finding enum value with Java 8 Stream API

I would use findFirst instead:

return Arrays.stream(Type.values())
            .filter(e -> e.s.equals(val))
            .findFirst()
            .orElseThrow(() -> new IllegalStateException(String.format("Unsupported type %s.", val)));

---

Though a Map could be better in this case:

enum Type{
    X("S1"),
    Y("S2");

    private static class Holder {
        static Map<String, Type> MAP = new HashMap<>();
    }

    private Type(String s) {
        Holder.MAP.put(s, this);
    }

    public static Type find(String val) {
        Type t = Holder.MAP.get(val);
        if(t == null) {
            throw new IllegalStateException(String.format("Unsupported type %s.", val));
        }
        return t;
    }
}

I learnt this trick from this answer. Basically the class loader initializes the static classes before the enum class, which allows you to fill the Map in the enum constructor itself. Very handy !

Hope it helps ! :)

The accepted answer works well, but if you want to avoid creating a new stream with a temporary array you could use EnumSet.allOf().

EnumSet.allOf(Type.class)
       .stream()
       .filter(e -> e.s.equals(val))
       .findFirst()
       .orElseThrow(String.format("Unsupported type %s.", val));

Arrays.stream(Type.values()).filter(v -> v.s.equals(val)).findAny().orElseThrow(...);

How about using findAny() instead of reduce?

private static Type find(String val) {
   return Arrays.stream(Type.values())
        .filter(e -> e.s.equals(val))
        .findAny()
        .orElseThrow(() -> new IllegalStateException(String.format("Unsupported type %s.", val)));
}