Iterate an Enumeration in Java 8

Question

Is it possible to iterate an Enumeration by using Lambda Expression? What will be the Lambda representation of the following code snippet:

Enumeration<NetworkInterface> nets = NetworkInterface.getNetworkInterfaces();

while (nets.hasMoreElements()) {
    NetworkInterface networkInterface = nets.nextElement();

}

I didn't find any stream within it.

Answer 1

_{(This answer shows one of many options. Just because is has had acceptance mark, doesn't mean it is the best one. I suggest reading other answers and picking one depending on situation you are in. IMO:}

• for Java 8 Holger's answer is nicest, because aside from being simple it doesn't require additional iteration which happens in my solution.
• for Java 9 I would pick solution describe in Tagir Valeev answer)

---

You can copy elements from your Enumeration to ArrayList with Collections.list and then use it like

Collections.list(yourEnumeration).forEach(yourAction);

Answer 2

If there are a lot of Enumerations in your code, I recommend creating a static helper method, that converts an Enumeration into a Stream. The static method might look as follows:

public static <T> Stream<T> enumerationAsStream(Enumeration<T> e) {
    return StreamSupport.stream(
        Spliterators.spliteratorUnknownSize(
            new Iterator<T>() {
                public T next() {
                    return e.nextElement();
                }
                public boolean hasNext() {
                    return e.hasMoreElements();
                }
            },
            Spliterator.ORDERED), false);
}

Use the method with a static import. In contrast to Holger's solution, you can benefit from the different stream operations, which might make the existing code even simpler. Here is an example:

Map<...> map = enumerationAsStream(enumeration)
    .filter(Objects::nonNull)
    .collect(groupingBy(...));

Answer 3

Since Java-9 there will be new default method Enumeration.asIterator() which will make pure Java solution simpler:

nets.asIterator().forEachRemaining(iface -> { ... });