8 February 2016
Objects vs. data structures
Several popular statically typed programming languages, including C++, Java and C#, have a serious design flaw. They make no useful distinction between objects in the OOP sense and plain data structures.
A plain data structure should only be a dumb container for data. It should not have any behaviour, only simple accessors for data items in it. It should not be possible to override data accessors. It should be clear and transparent what it does.
3 August 2015
Typesafe’s Reactive Straw man
In their quest to promote Reactive, Typesafe is beating up a straw man by portraying blocking I/O in a particularly stupid way which is rarely (if ever) done in practice.
In a recent webinar, I found this slide which suggests that a blocking I/O operation will waste CPU time while waiting for the I/O to complete.
If I understand it correctly, it does not actually work like this in any reasonable runtime environment / operating system.
21 July 2015
Leafpad > gedit
I want a simple, fast and lightweight text editor for my Linux desktop. I don’t want to learn a lot of new arcane key bindings, so not Vim or Emacs. I want a real GUI desktop application, not a console based one, so not nano (even though nano is nice when you only have a text console available). I don’t want a full-blown IDE for programming (I already have that) so I don’t need syntax highlighting and similar features.
11 June 2015
How to fix keyboard layout in Ubuntu 14.04
I regularly use Swedish keyboard layout, but I keep the English layout around in case I would like to temporary switch to it.
Ubuntu 14.04 sometimes mess this up and I suddenly get English layout when I log in. I fix this by installing dconf-editor, go to desktop/ibus/general, and make sure that the values engines-order and preload-engines are the same and in the desired order with the default layout first.
16 May 2015
Custom Preference for Android
I need a setting with a numeric value in my Android app. There is no obvious fit among the standard Preferences in Android, so I decided to implement my own Preference subclass.
This was a bit more involved than what I hoped for. I ended up with this. An improvement would be to be able to configure min and max values through XML attributes.
public class NumericPreference extends DialogPreference { private static final int DEFAULT_VALUE = 0; private NumberPicker mWidget; private int value = DEFAULT_VALUE; public NumericPreference(Context context, AttributeSet attrs) { super(context, attrs); setDialogLayoutResource(R.
26 December 2014
Running Adobe Lightroom 4.4 in Ubuntu 14.04
I use Adobe Lightroom 4.4 for photo editing. There is one very annoying aspect of this program, it is not available for Linux (only for Windows and Max OS X).
In order to run Lightroom on my computer, I had to use VirtualBox and install Windows 7 in it. This works, but is quite clumsy and annoying. And since Lightroom is the only reason for me to run Windows, I would like to get rid of it.
26 October 2014
Create a self-contained .jar file with Maven
If you want to create a self-contained .jar file, with all library dependencies included, you can do it with Maven. Include this in your pom.xml:
<build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-assembly-plugin</artifactId> <version>2.4</version> <configuration> <archive> <manifest> <mainClass>com.yourcompany.youapp.Main</mainClass> </manifest> </archive> <descriptorRefs> <descriptorRef>jar-with-dependencies</descriptorRef> </descriptorRefs> </configuration> <executions> <execution> <id>make-jar-with-dependencies</id> <phase>package</phase> <goals> <goal>single</goal> </goals> </execution> </executions> </plugin> </plugins> </build> Then when you run mvn package, you will get a target/*-jar-with-dependencies.jar file which you can run with java -jar.
2 October 2014
Running Jetty as a service in Ubuntu Linux
Jetty is a popular open source Java application server. In order to run it as a service on a Linux server, they recommend using a horribly overcomplicated and quite fragile script.
In Ubuntu server, there is a better way. Leverage Upstart and its declarative job definitions.
First install Jetty into /opt/jetty and create a jetty user:
useradd --user-group --shell /bin/false --home-dir /opt/jetty/temp jetty Then create a file /etc/init/jetty.conf with content like this:
5 June 2014
Don’t use large BLOBs in MySQL from Java
The MySQL database can store large chunks of binary data (up to 1 GB) using the BLOB data types.
However, this does not work well if you access the MySQL database from Java (or any other JVM based language) using the MySQL JDBC driver.
The JDBC API supports an efficient stream based way to handle BLOBs, but the MySQL JDBC driver does not implement this properly. It works, but it will buffer all data in memory in a way which is very inefficient and can make your JVM run out of memory if the BLOBs are large.
4 March 2014
Don’t use PipedOutputStream on Android
I was using java.io.PipedOutputStream in an Android app. The app performed horribly bad. After doing some profiling, it turned out that the call to PipedOutputStream.write(byte[]) that was really slow. After digging into the Android source code, I discovered that PipedOutputStream.write(byte[]) was not implemented, it just delegated to the default implementation in OutputStream which iterate through the array and call PipedOutputStream.write(byte) for each byte.
Since PipedOutputStream.write(byte) does some synchronization and Object.notifyAll() each time, it is really slow to do this 1000 times when you write a block of 1 KB data.