Thursday, 27 July 2017

Do interfaces inherit from Object class in java?

I was thinking this question suddenly at work...

Quick, Batman! To the StackOverflow1!!!

The answer comes straight from the JSL2.

References

[1] StackOverflow - Do interfaces inherit from Object class in java
https://stackoverflow.com/questions/6056124/do-interfaces-inherit-from-object-class-in-java
[2] JLS Java 8 - 9.2. Interface Members
http://docs.oracle.com/javase/specs/jls/se8/html/jls-9.html#jls-9.2

Thursday, 20 July 2017

mount: unknown filesystem type 'exfat'

When attempting to mount a USB drive, I encountered the following error regarding the filesystem exFAT1:
mount: unknown filesystem type 'exfat'
I had to install fuse-exfat as detailed according to [2].
# yum install fuse-exfat
Redirecting to '/usr/bin/dnf install fuse-exfat' (see 'man yum2dnf')

Last metadata expiration check: 0:00:02 ago on Fri May 12 07:06:52 2017.
Dependencies resolved.
================================================================================
Package        Arch       Version             Repository                  Size
================================================================================
Installing:
fuse-exfat     x86_64     1.2.5-1.fc25        rpmfusion-free-updates      40 k

Transaction Summary
================================================================================
Install  1 Package

Total download size: 40 k
Installed size: 71 k
Is this ok [y/N]: Y
Downloading Packages:
fuse-exfat-1.2.5-1.fc25.x86_64.rpm              335 kB/s |  40 kB     00:00    
--------------------------------------------------------------------------------
Total                                           118 kB/s |  40 kB     00:00     
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
Installing  : fuse-exfat-1.2.5-1.fc25.x86_64                              1/1
Mounting after that worked flawlessly.
# mount /dev/sdb1 mydrive
FUSE exfat 1.2.5

References

[1] Wikipedia - exFAT
https://en.wikipedia.org/wiki/ExFAT
[2] Mounting EXFAT formatted pendrives in fedora linux
https://coderwall.com/p/nvwgea/mounting-exfat-formatted-pendrives-in-fedora-linux

Thursday, 13 July 2017

Enumerations in EclipseLink

I have a field in the database that does not match with an Enumeration.

So I needed to do a little conversion in EclipseLink, and I didn't know how.

Below is the answer on that one.

References

EclipseLink - @ObjectTypeConverter
https://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Mapping/Basic_Mappings/Default_Conversions_and_Converters/ObjectTypeConverter
EclipseLink - EclipseLink/Examples/JPA/EnumToCode
https://wiki.eclipse.org/EclipseLink/Examples/JPA/EnumToCode

Thursday, 6 July 2017

Lambdas, New IO, and parsing textfiles in a hurry.

Okay, so I needed to do some parsing of a file containing URLs (which I "wget"-ted) and moving the retrieved files to proper locations.

I decided to write a quick Java program to do this instead of messing around with scripting languages or a Linux bash shell.

It worked very well, and I am rather pleased with the result and Java 8.

It contains the following "new/newer/not-very-old" stuff:
  • a lambda
  • a stream (of Strings)
  • a method reference (used as a lambda)
  • the java.nio.file package (New IO)
One small note: lambdas implement an interface. In this case the forEach requires a lambda that implements the Consumer interface. The Consumer interface does not specify an IOException. Therefore, I am required to catch it here and rethrow it unchecked.

References

[1] Java SE 8 - Official Javadoc
https://docs.oracle.com/javase/8/docs/api/