• No Spring One for me.

    Shortly after signing my job contract with Pivotal, my awesome boss told me to reserve time in December 2017 for the Spring One, because it is the event where almost all the Spring developers meet once a year.

  • Multithreading with Reactor

    I recently started working with (ok, fooling around is a better wording) Reactor, a reactive library that gets used by the new reactive parts of Spring. I’m especially interested in how multithreading works with Reactor. So here is what I learned so far.

  • What's Your Next Language?

    A common recommendation for software developers is to learn a new language each and every year. While I consider this a little over the top, learning a new language from time to time is certainly a good idea, but what language should you pick?

  • Work Breakdown Structure vs Backlog

    Lately people keep telling me that things that are common practice in agile projects are done in waterfall based processes as well. And you know what? Some are. But others aren’t and again others are completely missing. So lets make a loose series of articles about waterfall artifacts and practices compared to matching agile artifacts and practices.

  • New Version of Degraph

    Last week I produced a new release of Degraph! Yeah. Unfortunatly I did not fix the most pressing issue: You still can’t filter dependencies that you know are causing violations. :-/

  • Architect or Architect?

    I recently discovered that there are two very different types of people in large companies, who (at least in case of my customer) both claim to be “architects”.

  • Critical Skills for Software Developer too few People talk about

    There are many discussions of what you should learn or need to know as a software developer. Most of the time these discussions are about technical stuff, like IDEs, programming languages, patterns, tools and so on. Of course there are also discussions about soft skills: How to give feedback, how to deal with difficult coworkers or customers. All important stuff.

    But there is something in between. That's what this article is about.

    Take tiny steps: I spend a lot (read: too much) of my time on stackoverflow answering questions. And very often I find questions of people being completely lost in the mess they created. You can often tell simply from the tags they use. If they combine things like jsf, cdi and hibernate they obviously haven't the slightest clue where even their problem is. They created 5 different files for 3 different frameworks and now something doesn't work. Many very experienced developers will have a hard time setting up their preferred persistence framework, front end framework, build tool, DI-framework and what not in one go. So no surprise they failed. But how does a seasoned developer do this kind of thing? What is the advice?

    Walk with tiny steps! Actually, at first don't move at all. Think: What is the smallest possible change to the code base that can give you working code that is a little closer to your goal? If this involves changing more than 10 lines of code, keep thinking until you have a better idea.

    Now make that step.

    STOP! Look around. Did it work? If not you have at most 10 lines to worry about, ok I give you another 3 for possibly missing changes, but that's it. And a tiny step never includes front end, back-end, and domain logic at the same time.

    Understand stacktraces: This one comes again from stackoverflow questions. Actually from two kinds of questions. The one kind goes like this: "My code is broken, please help." The other kind looks like this: "When I do x my application fails with this error message:

    Application failed with XNotSupportedException in line 11, do y instead.

    Yupp: the first kind didn't even realize that a call stack might be important, the other kind didn't bother to read it. I know error message can be intimidating and hard to understand. But a lot of work goes into these things and for a good reason: Learn to read them. You need to understand every single line of a stacktrace. If you have problems with a line, there is probably a stackoverflow question about it. Find it and read it.

    Create and test theories: Developing software is an art. But it also has a lot of scientific work to it. And science works like this: You make an educated guess about something, and then you cook up an experiment to test it. (This is how Feynman defined it, and if you don't know Feynman you should fix that too.)

    The art part is back in the game when it comes to creating good theories. Good theories are easy to test. If you need a week to test a theory, you might want to test other theories first.

    Good theories have a good chance of being true and of being false. A theory that is false with high probability is just a stupid idea and a theory that is certainly true is also known as a fact we already know. Everything in between allows us to learn about the problem at hand.

    The term "Theory" might sound scary and complicated but it is actually rather easy. Let me give you an example. Your application doesn't have an effect you are expecting. You inspect the code involved where a method gets called which should cause the effect. An obvious theory would be: "That method never gets called", Another one, kind of the opposite: "The method does not cause the effect" a third one might be: "The effect does happen, but you fail to observe it due to some other problem". If you like me a couple of years ago you don't even think about this kind of stuff, because it seems so obvious and natural, but trust me: I have seen people randomly editing code trying to fix bugs with some kind of simulated evolution: apply random changes until the chances of survival increase. It seems like these developers forget that evolution involves as an essential part the death of millions of specimen ...

    Ask good questions: I consider the previous three points to be a precondition for being able to ask good questions. If you need more tips, go here.

    Abstract: This one might be the one most difficult. At least it is difficult to teach. Software development is about abstracting over things. A small child can add two specific numbers, using their fingers. Describing the algorithm they use without reference to specific numbers is programming (and a little more difficult).

    I consider my time as a physics student an excellent training for this. Boy was it abstract at times. Sometimes it was so abstract, we literally didn't know what we were talking about. But you can hardly expect people to study physics just for this. One thing that might help is learn different languages, because different language can easily abstract over different things. Learning this different ways to abstract over stuff will help you to abstract over your next problem in a meaningful way. Oh, and if a coworker keeps replacing pages of your code with 5 lines of her code, you know whom to ask for mentoring.

    Be Curious: We all have copied code from we found using our preferred search engine. That is OK. In some cases it is even OK to use the code without really understanding it. But when you use the same kind of construct over and over again you must stop and ask yourself: How is this sh*t working? This applies in all directions: Those weird JPA annotations, that fancy Javascript module pattern, the garbage collector, a compiler. Of course as you move further from your domain your understanding will be more superficial and more limited. Most of us Java Developers hardly know anything about how CPUs actually work and that is ok. But that mocking framework you use every day, I'm absolutely convinced that at least in principle you should be able to recreate it. And it is not that difficult. Just pick every day or at least every week, one thing that you use regularly and look up how it works.

  • How to Create a Legacy Code Kata Source Code

    From time to time I do a Clean Code Workshop for coworkers or customers. A large part of these workshops deals with legacy code. I always start with the Ugly Trivia Game by J. B. Rainsberger, which actually isn't by him, but I use his version anyway. While it is a great resource it gets boring after you have reviewed, tested, refactored, tested it some more and reviewed the tests and refactorings. Also: does it really look like the average legacy code we find in our projects? I don't think so. Real life legacy code has more dependencies and does more really stupid stuff. My favorite so far was a class that loaded stuff from the database in the constructor. Not fun.

    Therefor I like to create a little code base for working with legacy code that is very realistic but still small enough so one can handle it in the setting of a workshop and it is actually really simple to do that:

    First pick some class that is ugly. Big methods are great. Sometimes you come a cross classes that are super tangled with 2-5 other classes. Those are super awesome. Don't pick anything to large. A class with 5000 lines just create more work, not more learning opportunities.

    Second copy that class (or that small class cluster) in a new project. No dependencies, none of the other stuff it works with. Most likely it wont compile, we gonna fix that in the next step.

    Third fix all the compile problems using one of the following approaches:

    • Just add simple libraries like logging or Apache commons to the project.
    • Create missing classes using your IDE, will all the right methods. If the methods look like getter and setter, actually make them getter and setter.
    • If the methods look more complicated just throw a SomethingTerribleIsHappeningHere exception.

    This is really fast, works with 98% of all legacy code I came across so far and creates some mean challenges for working with legacy code.

  • Checklists for the win!

    I recently read "The Checklist Manifesto" and boy was it a great read.

    First it was fun to read! Checklists sound like the manifestation of boring, right? How about a story of surgeon who takes care of a minor flesh wound, when the blood pressure of the patient suddenly drops to almost zero. Cutting the patient open the surgeon finds the body filled with blood! Now if checklists are deemed appropriate for avoiding stories like this, they suddenly aren't that boring anymore, right? And the book is full with stories like this. If you imagine stories that you read visually and can't look at blood, sorry, this book isn't for you. Everybody else: Go get and read it.

    Professionals of various kinds use checklists. Medical doctors, Pilots of course and many more. Yet many people claim they don't need checklists. They are smart enough to do the right things. Their job is too complicated to be pressed in simple checklists. Really? So the job of a pilot is somehow "simple"? Or that of a surgeon? Of course it isn't. But still there are many things that are actually rather simple. And it is rather difficult to not forget about those. That's when checklists help.

    Since I finished the book I established two checklists for myself:

    One checklist I go through every morning at work. It looks something like this (without the italics, those are just for you so you can make sense out of the few words) and is written on a post-it taped to my monitor:

    • Check mail. Yes I'm proud that sometimes I'm so focused that I don't check mail at all, so I need it on my checklist
    • Check calendar. To make sure I'm aware of all important appointments today
    • Check logs. Of all servers, so if there is a new problem, I learn about it.
    • Check Jenkins. Mail notification doesn't work, too much E-mails.
    • Fill out time sheet. In the morning I remember what I did yesterday and I can enter the time I started to work.

    The second checklist is for debugging problems with dependency injection. As much as I like the Springframework, from time to time it complains about being unable to instantiate a bean, because a dependency is missing, although the bean is right there in my IDE. For this I created a checklist that lists all the various possible reasons for this problem:

    • What exactly is the problem described in the stacktrace. No bean of matching type? Or no bean of matching name? Or more than one bean?
    • Is the bean that should get found in the correct source path I have a history of putting beans in test instead of main
    • Does the bean that should get found implement the correct interface? Here it is important to check the full name
    • Does it have the correct name?
    • Are the scopes compatible? I'm not sure if this will actually result in the same problem

    I store this one in Evernote and will pull it up when I get this kind of problem the next time.

    The first checklist already proved highly useful. The second has still to be tested. I just created it when I tried to fix just that kind of problem the last time.

    What checklists do you use?

    One last word: Of course as software developers we have an advantage. Many things that ask for a checklist can be implement as a program. So don't replace your automatic build with a checklist please.

  • Why I Won't Accept ANY Magic Number

    One of the first things I like to establish in a new project is the use of tools like Checkstyle and Findbugs in order to codify some code guidelines and to avoid bugs that can be determined by static code analysis.

    Sooner or later with these tools one stumbles over a case where people have the feeling it is going to far. One such case is the check for Magic Numbers of Checkstyle. It will warn about any use of numeric literals except -1, 0, 1 and 2 that aren't used to define a constant.

    Many developers have a problem with this check as one can see from the resulting code. I have seen code like this

    private static final int FOUR = 4;

    and also

    private static final int FOUR = 5;

    and my all time favorite (I'm not making this up!):

    firstname = rs.getString(1);
    lastname = rs.getString(2);
    city = rs.getString(2 + 1);
    zip = rs.getString(2 + 2);
    country = rs.getString(2 + 2 + 1);

    But there is a different case where the discussion comes up. It's with obvious constants like 100 for converting fractions into percent values or 1024 for conversion between bytes and kibibytes. Some argue these aren't magic numbers (or magic numbers but not as bad) because their meaning is obvious and they won't change.

    I disagree and will vote to make them constants any time. Here is why:

    1. The meaning is NOT obvious. What does value * 100 mean? Is a fraction converted to percent? Is a length measured in meters, converted to centimeters? Or something multiplied by a rough approximation of g*g with g being the gravitational acceleration on earth? Or maybe I'm multiplying something with the size of an array, that happens to be 100. Can't tell. A simple constant with a proper name will fix that.

    2. Ok, I do agree, many of these constants won't change. But the purpose of defining constants (or methods, or classes) is not (only) to enable later change, but to make reading, understanding and reasoning more easy. So the question if a value might change in the future is completely irrelevant.

    3. (This one is the argument that I'm missing in most of the discussions) I just don't want to think about it or have others think about it. I have seen dozens, probably hundreds of instances, where a properly named constant would have helped tremendously understanding a piece of code. And I have seen very few cases where it might have hurt readability and not a single one where it hurt badly. Therefore: just extract a constant and be done with it.

    Note: Just because it is a constant doesn't mean it has to be public, or even a class level field. If it is used only in a single method a local variable is just fine.


Wan't to meet me in person to tell me how stupid I am? You can find me at the following events: