Language Features Enhancing Trust

Alex just facepalmed.

if ( Boolean.TRUE.equals(employee.isHappy) ) {

“Wow, the human invention never ceases to come up with new ways to adorn boolean expressions! Too bad Eclipse doesn’t have a Quick Assist for simplifying them…”
Ah, one of those WWTC moments. That’s when the Show Annotation feature of Subversive comes in handy… which revealed that Bob is the author (unless he only adjusted the whitespaces in that line). “But he already left the office for today. Now, I’ll just simplify it and similar occurrences manually and tomorrow, I’m going to considerately mention to him that he could have written this condition umm… more concisely.” Alex pondered a bit over the commit message, but practiced self-restraint and wrote simply

Simplify boolean expressions...

(though he couldn’t help omitting those ellipses).
Next day, some of the tests of Bob’s module were failing.
– Hi Bob, could we have a look at your code? First, there are some red tests, and…
– Hmm, but I haven’t modified that module since yesterday. Let’s see the exception!
– Okay…

Exception in thread "main" java.lang.NullPointerException
at EmployeeLoader.loadEmployee(

“Hmm, exactly the line I modified. But…” – thought Alex.
– …how could a simple condition without a single dereferencing cause a NPE?! – asked Bob, confused just like Alex.
– Uh-oh, I think I have a suspicion… Please show the declaration of isHappy

private Boolean isHappy;

Alex facepalmed once again, but this time the cause was himself.
– NOOO! The dreaded autoboxing! But again, why isn’t it a primitive boolean?
– Hey, now I remember! Employees are parsed from XML using an autogenerated schema. The attribute isHappy is optional, so it might very well be null.
– Sorry, Bob. I feel silly for acting without asking you in advance or running the tests before committing. See, I couldn’t have imagined how this kind of change could break.
– Take it easy, Alex. 🙂 Now you can. In fact, I thought Boolean.TRUE would refer to the attribute’s type being non-primitive unambigously, and the Yoda condition would evoke the possibility of the null value immediately.
– I understand you, but to avoid such misunderstandings in the future, would you mind writing

if ( (employee.isHappy == null) && employee.isHappy ) {

to make it totally explicit that isHappy can be null? Or rather set an optional false value for this attribute in the schema?
– OK, I’ll consider.
Fortunately, Bob took the incident very lightly and his commit message was just:

Revert Alex's "simplifications" :)

The first thing Alex did was to set a warning for boxing and unboxing among the Java compiler settings. As he was accepting the changes, he thought: “Null and primitive types as well are billion dollar mistakes coming from arbitrary language design decisions which reflect implementation details. But at least they tought me to trust my fellow’s code – or at least to inspect the types before refactoring.”

Hi-DPI Eclipse screenshots


A picture is worth a thousand words.

Recently I was writing a paper based on EMF-IncQuery, and I wanted to include some screenshots. For good reasons, a 300 dpi photo was recommended, but that represents quite large resolutions for reasonably sized images. Although I couldn’t always get this resolution, but I found some nice tricks to use for later.

Eclipse always allowed configuring some fonts – some time ago I experimented with the theming capabilities of Eclipse 3.x, and could increase a few font sizes, but some widgets such as list or tree viewers did not support such theming.1

GMF-based editors, such as the Papyrus UML editor or the Ecore Diagram editor provide support for exporting the diagram in PDF format – a format that retains (most2) graphical information of the diagram in a vector-graphic format, usable for inclusion in LaTeX documents.

The multitouch zooming support for Zest graphs also helped a lot for screenshots, as I could simply use all available screen area to get a nice shot. Even for graphs that do not contribute their Zoom Managers to the user interface.

Finally, OSX already supports Hi-DPI modes for its entire operating system (dubbed Retina Display), that can also be enabled on non-Retina displays with some hacking: basically by downloading the Quartz Debug program (details for Lion and Mountain Lion) I can reduce the visible resolution to 960×540 pixel on my Full HD monitor. It also supports the use of one monitor as HiDPI and the other as normal – that comes quite hand with applications that do not support HiDPI mode (such as Eclipse out of the box, or Firefox).

OSX supports HiDPI modes

One big issue was that Eclipse 4.2 does not support HiDPI resolutions out of the box. Luckily, this was already evaluated in Bugzilla, and in a corresponding Stack Exchange entry.  Basically, the info.plist file3 of the has to be updated to state it supports High DPI mode, and then the Application itself moved in order to OSX detect the changes.

As a result: Eclipse sees that it has a limited amount screen estate, while in practice it uses 4 times as many pixels. While it is not usable at all for everyday programming, it helped a lot for screenshot creation.4

A low DPI version of a small screenshot
A HiDPI version of the same editor

Alltogether, there are various ways to create high definition screenshots in Eclipse. It helps knowing them and using accordingly. For this reason, I am curious what other ways are there to create screenshots with high resolution – how do you do it?

  1. Note to myself: I want to experiment with the 4.x theming capabilities, and update the presentation theme to work with the CSS-based themes of e4. []
  2. However, I did see some interesting glitches related to the background settings of Ecore Diagrams… []
  3. By the way, the XML syntax of the plist files is something awful – it reminds me of the parameter handling in shell scripts or console applications – odd numbered parameters are the keys while even ones are the values. Not that XML allows the definition of attributes or inlined elements – but who cares? []
  4. Except when using Skitch – a nice screenshot manager app. But it does not know about the underlying HiDPI mode, and always created a low DPI shot. []

EMF-IncQuery: First public release

One of the most common tasks when working with models is executing queries on them (e.g. finding a set of corresponding model elements for code generation or finding violations for model constraints) – quite often repeatedly. To allow effective calculation and recalculation, an index of the EMF model has to be created and maintained during editing operations.

EMF-IncQuery is a tool we are developing at the Budapest University of Technology and Economics try to solve this issue by providing a runtime library for these indexes, and additionally an Eclipse-based tooling to specify and debug such queries. I have already blogged about a validation framework based on this technology, and my collegue, István Ráth gave a short presentation in last year’s EclipseCon Europe Modeling Symposium.

However, previous tool demos were held using a tooling and query language originally created for the VIATRA2 model transformation framework, so it was somewhat hard to use. Since these demonstrations we created a new, Xtext-based tooling using a modified query language that fits the EMF model specifications better.

The Xtext-based editor with type information hovers.

Another new user interface component is the Query Explorer: a view that allows evaluating developed queries without using the generated code in a new Eclipse instance, while allowing the reuse of existing domain editors.

The Query Explorer can be used to evaluate patterns using existing model editors.

As for examples, since last year we developed two new case studies for EMF-IncQuery:

  1. Derived features allow the creation of EMF derived features based on incremental queries as backend;
  2. We also created connectors for JFace databinding for query results allowing query-backed automatically updating user interfaces.

Even better, this new version is available since Wednesday – for a detailed release notes see the announcement post in our homepage. If you want to download this release, you can use the Eclipse Marketplace client (at least if search is working as expected – today we managed to not find our software there using the built-in search 🙁 ). Alternatively, EMF-IncQuery is available from our update site:

Alltogether, the new EMF-IncQuery release marks an important point: we believe at this point, it is ready for use. For me, this is an important checkpoint, as in the last year I put a considerable effort of getting this rolling.

As for the future, EMF-IncQuery is on its track to becoming an Eclipse project: the creation review is scheduled for the 10th October 2012. After the creation, we plan to migrate our codebase, and have of course further ideas on how to improve the system to be usable in more and more cases.

Lesson of the day: Beware the indirect dependencies in Eclipse 4.2

Executive summary: If you cannot move or minimize your views in Eclipse 4.2, always check whether the org.eclipse.e4.ui.workbench.addons.swt bundle is present in your run configuration.

A view misses its minimize icon

Today Eclipse surprised me with a nice feature. I tried to reconfigure my runtime workbench to create some screenshots, but I couldn’t. The views were missing the minimize button, and dragging view parts between groups did not work.

I had some minor issues with the new workbench model, so first I tried to check everything is at its base setting. I reset the perspective, closed all perspectives, restarted the workbench, but nothing helped. Finally, I noticed a short error message in the Error log:

Unable to retrieve the bundle from the URI:

That provided the required hint: to conserve memory, I usually start a runtime Eclipse with a reduced set of plug-ins – possibly a dependency is missing. Looking at the uri from the error message, I found, that the org.eclipse.e4.ui.workbench.addons.swt plug-in was not added to the Run configuration. I checked the corresponding box, and voilá – everything worked as expected.

What makes this case more interesting is that the built-in dependency validation report no issues. I had my own debugging sessions because of missing dependencies, so I set all my Run configurations to validate every dependency at startup. This means, this plug-in is not needed for executing the platform (technically true), however, when it is missing, it strongly reduces the usability.

Alltogether, what I am missing is some kind of higher-level validation that could report such issues. But in the meantime, I publish this, hoping, someone else finds it useful.

DIY musical doorbell

A doorbell is not the most important equipment of a home, however it is necessary and it still matters in a way. It is the thing that makes the first impression of your home to any visitor. The standard school-bell type doorbells hurts the ears and freaks out everyone who dares to touch the button and anyone who is unfortunate to be home at the time. A musical doorbell can be really expensive and the sound of the cheaper ones are simply annoying. Why not try to build one at home?


It can be easier than it seems at first glance. Almost every part of it can be found in the drawer of an average hardware hacker:

  • Any speaker scooped from an old PC
  • A cheap MCU
  • An NPN transistor
  • An 1K resistor
  • Optionally a potmeter for volume control
  • 4 diodes
  • 2 capacitors
  • An 5V linear regulator (L7805)

The theory of operation is really simple: the MCU drives the speaker with a square wave on an arbitrary frequency to make a sound. Because the MCU usually cannot bear high current enough to make it loud, a transistor is used to drive the speaker.

The power source may be a standard bell transformer, which makes 12V AC from the 230V AC. In my case it was given as in our apartment building there is one generator for more apartments. To provide a stable 5V for the MCU, a simple Graetz-bridge can be used along with a linear regulator.

Doorbell schematic (
Doorbell schematic (


The software part is just as simple. The first problem is to make the proper frequency for the square wave output. The simplest approach for this is to use a timer integrated into the MCU, and toggle the output on the timer interrupt. Now the frequency can be set by the timer options.

The other task of the MCU to switch the settings of the mentioned timer after a time to make a series of sounds. I’ve used another timer to interrupt in every ~0.2sec, which decrements a counter to determine the delay for the sound. If the counter reaches zero, the new timer settings and delay counter are loaded from the program memory tables.

Calculation of timer settings

The music you want the bell to play, is a series of sounds with determined frequency. This must be converted to a series of timer settings. For the PIC16F1824 I’ve used, this settings includes the compare register value along with the pre- and postscaler settings. To determine the best settings for each sound frequency (best = real frequency closest to nominal within the available set of register values) is a straightforward task, but requires a lot of calculations. It is much easier to write a script that makes all the calculations and generates the proper code tables for the program. This way it is easy to change the music to whatever you want.

Finish the bell

All is left is a bit of soldering and putting it in a suitable box:
The finished doorbell