Adding method shells from the assignment

1 job for master in 1 minute and 21 seconds (queued for 1 second)
Name Stage Failure
maven_build Test
[ERROR]   location: class com.ds.fifthassignment.Stack
[ERROR] -> [Help 1]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1]
ERROR: Job failed: exit code 1