[Java] ensure java implementation meets clarified dictionary spec

[asfimport]

see parent issue.

 

CC @tianchen92

Reporter: Micah Kornfield / @emkornfield
Assignee: Ji Liu / @tianchen92

PRs and other links:

• GitHub Pull Request #5945

_{Note: This issue was originally created as ARROW-7284. Please see the migration documentation for further details.}

[asfimport]

Micah Kornfield / @emkornfield:
Issue resolved by pull request 5945
#5945