Iterate an Enumeration in Java 8

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

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

In case you don’t like the fact that Collections.list(Enumeration) copies the entire contents into a (temporary) list before the iteration starts, you can help yourself out with a simple utility method:

public static <T> void forEachRemaining(Enumeration<T> e, Consumer<? super T> c) {
  while(e.hasMoreElements()) c.accept(e.nextElement());
}

Then you can simply do forEachRemaining(enumeration, lambda-expression); (mind the import static feature)…

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(...));

_{(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)

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

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