How about this comment:
"""
Transform an input string like hdfs://host:port/dir, hdfs://host:port, /dir
into a pair of address and path. The returned pairs are ("hdfs://host:port", "/dir"),
("hdfs://host:port", "/"), and ("", "/dir"), respectively.
"""

For input "/dir", how about returning ("/", "/dir")?

Also, the return type can be "Pair<String, String>". We have a Pair<?, ?> type in Tachyon.