Wednesday, October 27, 2010

Kanban in IT

Here's a nice series of articles on using Kanban in an IT setting. I found it interesting because it shows not only what they did, but how their process evolved over time in several settings.

Saturday, March 20, 2010

Sucking Less: Checking In More Often

I'm fairly fearless when coding, which means that about once a week, I delete a huge chunk of something I should've kept, or change something into something unrecognizable, thereby inadvertently breaking a dozen unit tests. When I discover the problem, usually about 4 hours later, I no longer have any idea what I did that made the bad thing happen. Then I spend another 2 or 3 hours figuring out what I broke and fixing it.  Ugly.

On my personal projects, I check in code every time I get a unit test working. My checkins are something like 15-20 minutes apart.  On projects I get paid for, though, checking in means running the whole unit test suite, and that can take 10 minutes (on a good project) or 2 hours (on a bad one)--so I don't do it very often. That's when I get into trouble.  I've been meaning to solve that problem for some time, and Joel Spolsky's blog topic last Wednesday (Joel on Software) finally kicked me in the pants.  It took 15 minutes to solve the problem; here's how I did it.

Wednesday, March 3, 2010

Annotating Custom Types in Hibernate

Hibernate has a lot of nice features, and it's pretty well documented, but a recent need to add a simple custom type to an existing mapping left me flailing around for documentation on exactly how to do it. I wanted to do it with annotations, not by updating the Hibernate configuration (that approach is well-documented). Here's how it's done.

Sunday, February 21, 2010



The proposed class, java.util.DuctTape, is designed as a general purpose fix for a variety of commonly-observed situations in production code. It serves as a temporary patch until a permanent solution is developed and deployed.

Wednesday, February 17, 2010

Database/Code impedance mismatch

I love natural keys in database design. You have to pay attention, though: the natural impedance mismatch between a programming language representation and the database representation of the key can bite you.

Consider an object whose primary key might contain a date--say, a change log record. Oracle and DB2 both store a DATE as a time containing year, month, day, hours, minutes, and seconds. No timezone. The natural mapping for a Java tool like Hibernate is to map to a java.util.Date, which stores the Date as a time in milliseconds since the epoch GMT, and then maps it to whatever timezone is set on the machine where the code is running for display and conversion.

Now consider what might happen (especially if our change log record is attached to some parent object);

  1. We create and save the object; it is persisted. The local cached copy contains a non-zero value for milliseconds, but the database has truncated the milliseconds value and saved it.
  2. Later on in the code somewhere, we have reason to save the object again, perhaps as part of some collection operation.
  3. Hibernate looks in its cache, compares it with the database, and notes that the values of the Date don't match--so it tries to save the value again.
  4. The database dutifully tosses out the spare milliseconds, and bam! we have an attempt to re-insert an existing record, so it throws an exception.
This is all terribly confusing to the programmer, who, inspecting the objects in question, sees no difference between what's in the database and what's in her code, especially since the default display characteristics of her database browser and her debugger don't show the milliseconds.

The easy fix in this case is to declare a class which matches the database representation--in this case, a good choice would be to declare a new class which truncates the milliseconds. A modest example is shown below:

* Public Domain; use or extend at will.
import java.util.Date;

public class DbDate extends Date {
/** increment if you change the state model */
private static final long serialVersionUID = 1L;

/** @see java.util.Date#Date() */
public DbDate() {
long t = getTime();
setTime(t - t%1000);

/** @see java.util.Date#Date(long) */
public DbDate(long t) {
super(t - t%1000);

/** @see java.util.Date#setTime(long) */
public void setTime(long time) {
super.setTime(time - time%1000);

Also note that if you declared the database column as a TIMESTAMP, the Java and database representations more-or-less match--avoiding, in this case, this kind of problem. Note that Oracle doesn't support TIMESTAMP_WITH_TIMEZONE in a primary key, and DB2 doesn't implement TIMESTAMP_WITH_TIMEZONE at all--as of the last time I had access to DB2.

Dealing with timezones is another topic entirely--one which I'll take up in a future post.

Sunday, February 14, 2010

Limiting Irreversibility

This afternoon I was reading Martin Fowler's commentary on architecture:, and ran across the following:

At a fascinating talk at the XP 2002 conference (, Enrico Zaninotto, an economist, analyzed the underlying thinking behind agile ideas in manufacturing and software development. One aspect I found particularly interesting was his comment that irreversibility was one of the prime drivers of complexity. He saw agile methods, in manufacturing and software development, as a shift that seeks to contain complexity by reducing irreversibility—as opposed to tackling other complexitydrivers. I think that one of an architect’s most important tasks is to remove architecture by finding ways to eliminate irreversibility in software designs.

I think he's absolutely on the mark with this--in fact, I think it illuminates one of the two or three key roles of architecture in system implementation. If the architect focuses on helping to define approaches which are hard to change once the system "complexifies", and in helping developers write solid code that can easily be modified when needs change, (s)he goes a long, long way towards making the system flexible and maintainable.

Note that there's two architectural roles there: (1) helping to make key decisions early, and (2) mentoring developers around those decisions.

On most of the dev teams I've worked with, the first set of decisions is made by proposal and refinement--one of us proposes an overall approach, and the rest of us point out tweaks or whole new approaches until the whole thing gels in everyone's mind. It seems to work, if everyone is engaged. Some architects would prefer to "rule by fiat", but I've found that generally results in systems which can't be maintained or in far more work than is needed. It's very hard to get key decisions right by yourself. To illustrate: I once proposed a relatively modest refactoring in a large thorny user interface, to separate business logic from display logic and generally make it easier to maintain. The reigning architect decided we needed a complete rewrite, in direct opposition to the opinion of everyone else on the team. Nobody objected strongly, though everyone quietly agreed that a rewrite probably wasn't needed--it's lot more fun to write new code than to modify old. Nobody asked what the minimum effort needed to meet the requirements was. About two years and a couple million dollars later, the new system is, indeed, quite a bit better-structured than the old one. It's not clear if the new UI will produce allow faster, cleaner updates than the old one--but it sure cost a lot to build: about twice the initial estimate, and about 6 times the original proposal. (By the way: the rewrite is considered a success by all involved. See "What Could Possibly Be Worse Than Failure?" by Alex Papadimoulis.)

A second role implied in minimizing irreversibility is "mentor". Writing good code is hard; writing well-structured code without someone to bounce your design off of is doubly hard. I spend a lot of time talking with the members of my teams, trying to make sure we have a design that's flexible and understandable. A lot of what we think of as "architecture" starts out as a small feature being implemented by a relatively junior developer. I try to make sure (s)he has someone to work with in the early stages of that work, or at least a trial design to start from.

I love Martin Fowler's writing: he always gives me something good to think about.

Wednesday, February 3, 2010

SEMAT and development principles

My first reaction to SEMAT was--is this practical? But as I've thought about it more, I've decided there are some principles of good software design and implementation they can probably agree upon and illuminate.

For context: I spent 15 years as a practicing nuclear engineer before becoming a practicing software developer.

"Engineering practice", as I found it in the field, is often as arbitrary as "software development practice". What is "good" is measured first by "what works", second by "what's elegant", and finally by "what's inexpensive", and is judged primarily by senior practitioners working against their own experience rather than some set of objective standards (though those exist as well). In hardware engineering, the time lapse between design review and implementation is quite often very long (especially large-scale design, e.g. power plants, where I worked). As a result, feedback loops are even longer and harder to manage. What dominates in the large scale seems to be "what worked"--and just as often, "what failed".

This seems to me to be exactly the type of thing we're developing now as developers--we now have lots of categories of languages for solving different types of problems and we're developing solid tools and techniques for measuring performance, managing projects, and closing the loop between design and implementation. The world for software developers is a FAR less arbitrary place, and has far more development of tools and techniques, than in 1976 when I started coding.

The body of common practice is regularly changing in hardware engineering, as analysis tools get better. When I graduated, one of my first tasks required a stress analysis, which I did with a calculator by hand. These days, an engineer would set that up in a desktop finite-element analysis program with a nice UI, and he'd get a better answer in less time. The principles are the same, though: determine, through an understanding of material behavior and machine design, what a specific application required of the machine and what combination of off-the-shelf components and custom machining could be used to implement that application. It's very much what I do today: I pick off-the-shelf components and custom components to create a design to meet certain requirements.

Can we, as a group, specify some of the principles on which those decisions get made? I suspect we can. While I'm only really fluent in one sub-part of OO design, I know of a few; consider the SOLID principles in OO design, various common design patterns, and the corpus of tools and techniques in Knuth's "The Art of Computer Programming".

Sunday, January 10, 2010

Coupling Design and Implementation

Six weeks ago or so, our development team reviewed a small design change in the way status is managed by an object. Basically, we broke one state variable into four, and thought more carefully about the state transitions allowed and expected for the class in question.

Yesterday, one of our analysts, at the prompting of one of our developers and two of our data designers, reviewed a completely new take on the same design change... none of the guys in question knew about the previous design change (they'd missed the design review). We ended up going with the previously-reviewed design.

The whole meeting and the thought that led up to it could have been avoided if there had been some mechanism for ensuring the approved design was implemented. This bit of design, like all design, is pretty much wasted if it remains in design documents.

One way to handle this would have been to somehow automatically compare the existing design artifacts to the implementation to see if they matched, and complain if they didn't. Even if we didn't implement the approved design right away, then, there'd be a mechanism for reminding developers that they planned to do something one way, and haven't made it happen yet.

Thursday, January 7, 2010

Three snippets of "interesting" code

Here's a bit of code I use in interviews:

try {
if (foo())
return 1;
} catch (Exception e) {
throw e;
} finally {
return 3;

The questions I start with are:
  1. what does this do if foo()==true? If foo()==false? If foo() throws an exception?

  2. how could you recode this more simply?

  3. the original spec was:
    • if foo is true, return 1,

    • if foo is false, return 3,

    • propagate exceptions.

Provide code to implement the spec.

It's sobering to note that over 2/3 of interviewees for senior Java programmer positions fail all three questions. How would you answer them?

I firmly believe that even mid-tier developers should have no problem describing what they mean in code, and in understanding what others mean, even in code which is poorly written. There always seems to be a snarl somewhere that nobody wants to touch (I've written one or two of those myself). For the most part, though, the bad code I see is the result of "I'm not sure how to do this, but this seems to work".

Here's one such snippet:

static final BigDecimal ONE_HUNDRED_PERCENT = new BigDecimal("1.00")

This is just bad code, unless you're letting BigDecimal manage all the results' scales itself (we aren't, and you shouldn't; see my previous article on BigDecimal rounding). It's completely replaceable with "BigDecimal.ONE". It leaves the resulting code less clear, and performs no useful function.

I found the following code (paraphrased) in a Java application I'm working on:

foo(vc.getNewValue(), ppCorrectedValue=vc.getNewValue());

It's perfectly correct and exactly equivalent to:

ppCorrectedValue = vc.getNewValue();
foo(vc.getNewValue(), ppCorrectedValue);

That sort of expression is common in C; most C developers are aware that the equals operator evaluates to the left-hand value of the expression. Many Java developers aren't aware of this fact--so I was surprised to see it. I'm not sure it improves the readability of the code, though, so I'm refactoring it into the second form above.

Where I think the equals operator behavior really helps in Java is when setting up initial values:

i = j = 0;

Good code is hard enough to write; have pity on the next guy, and be as straightforward and clear as possible. Arabesques like assignment inside a function call parameter list just make your code harder to read and maintain.