Adjusted documentation of dbList command (Java)

[clovergaze]

• provided the correct return type
• extended the example

Reason for the change
I tried to get the list of database names from the server and the current documentation is not helpful in that regard. The specified return type is wrong and the array with database names had to be extracted from the Result<Object>.

Description
I corrected the return type and added a useful example that shows how to get the database names.

Checklist

• I have read and agreed to the RethinkDB Contributor License Agreement

[clovergaze]

This might also be a viable example:

try (Result<Object> result = r.dbList().run(connection)) {
  result.forEach(list -> {
    ((List<?>) list).forEach(System.out::println);
  });
}

[srh]

The return type should be array. The types in this section refer to ReQL types, not Java types.

[clovergaze]

Okay, I will revert that.

[srh]

I'm not familiar with the Java driver, but I think dbList will never be null. Unless RethinkDB returns a nil result.

[clovergaze]

In this example, my IDE (IntelliJ IDEA) complained that forEach could produce a NullPointerException and suggested adding this check.

In the end I did something more like this:

final Result<?> result = r.dbList().run(connection, List.class);

try (result) {
    List<?> databaseList = (List<?>) result.single();

    if (databaseList != null) {
        databaseList.forEach(System.out::println);
    }
}

So, maybe that should be the example code? People can still leave out anything they do not want or rewrite it according to their needs. My thought was just to provide a hint on how to use it. And maybe a more elaborated example could also lower the hurdle for new developers, to see how they could use it.

But of course the provided example should show a somewhat recommended way. For me r.dbList().run(conn); was not really that sufficient or telling and this is what I thought could have helped me in the first place to get to use it more quickly. This is code I use because it is robust, but any suggestions are welcome.. I am referring to the new code above.