Add support for jdk9 and jdk10

[javadev]

It may be new settings for travis-ci.

[PromanSEW]

Please add these new methods from Java 10:

A new method orElseThrow has been added to the Optional class. It is synonymous with and is now the preferred alternative to the existing get method.

https://docs.oracle.com/javase/10/docs/api/java/util/Optional.html#orElseThrow()

New methods toUnmodifiableList, toUnmodifiableSet, and toUnmodifiableMap have been added to the Collectors class in the Stream package. These allow the elements of a Stream to be collected into an unmodifiable collection.

https://docs.oracle.com/javase/10/docs/api/java/util/stream/Collectors.html#toUnmodifiableList() and other toUnmodifiable* collectors

Source:
http://www.oracle.com/technetwork/java/javase/10-relnote-issues-4108729.html#NewFeature

[aNNiMON]

@PromanSEW since toUnmodifiable* collectors use Java 9 List.of, the preferred alternative in LSA would be

Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList);

Unfortunately, Collections.unmodifiable* methods are added in Android API 24. I can't drop Android pre-24 support.

[PromanSEW]

@aNNiMON I have just checked, these methods exist in the source code of API 16 at least. I think they existed since older API than 16 too. Android documentation can contain errors, for example ConcurrentLinkedDeque was added in API 21, but I found this class in API 16 too. I think checking the source code of earlier APIs is a good idea.

[aNNiMON]

@PromanSEW you're right. I just check Android 2.3 source code and it has Collections.unmodifiableList. It's bad that Android documentation contains errors like this.

[javadev]

oraclejdk10 is also supported by travis-ci now.