Github user reudismam commented on the issue:
https://github.com/apache/giraph/pull/79
FileInputStream and FileOutputStream override the finalize method. As a
result, their objects are only cleaned when the garbage collector performs a
sweep. Since Java 7, programmers can use Files.newInputStream and
Files.newOutputStream instead of FileInputStream and FileOutputStream to
improve performance. finalize method is deprecated in Java 9+.---
