Andrae Muys provides some excellent advice on implementing Object.equals() however I do have to correct one thing. Andrae presents the code:

class A {
  int n1;
  public boolean equals(Object o) {
    if (!(o instanceof A)) {
      return false;
    } else {
      A rhs = (A)o;
      return this.n1 == rhs.n1;
    }
  }
}

and suggests that it is incorrect. It is not. This is absolutely, 100% the correct way to implement equals for that class. The alternative he presents on the other hand is incorrect:

I was fortunate enough to be invited out to a friends place to see the fireworks last night. They happen to own the penthouse apartment on the river front with an awesome view of nearly all the fireworks. The fireworks are launched from numerous sites along the river so being able to see all of them is really quite unusual. Better yet though, one of the launching barges is positioned directly in front on the balcony as if it were a private show just for us. That particular barge this year had some issues launching it’s fireworks. There were about three sections where all the other barges launched fireworks in unison but “our barge” sat there doing nothing. Apparently it was unplanned because at the end our barge suddenly started firing off every firework it had missed all at once. A display that was intended to take about 10 minutes was sent up in about a minute flat. Extremely impressive! Also impressive was the dump and burn which was close enough to feel the heat hit you and felt like you could just reach out and catch the plane. I’ve never been overly impressed by fly-bys when standing at ground level at South Bank but from the penthouse it really is quite an experience. Oh, and Iain has photos.

I’m currently wearing one of the shirts that James Gosling hurled into the crowd by various means which depicts Duke aiming a rocket launcher at a weird looking demon with four arms labeled complexity. Earlier today I was accosted by a very young man who asked what that was on my shirt. When I pointed to Duke and said “this guy’s called Duke” the response was: “he’s crap. I like this guy ‘cause he has four arms”. I’m not sure that’s the reaction the designer was after….

And they did. Went to see We Will Rock You – the musical by Queen and Ben Elton last night and it was sensational. The songs fit into the story line brilliantly and the story itself was interesting and not just an excuse for singing the songs. The constant use of song references as bad puns just added to the experience for me and it was particularly impressive to see the customization for the Australian audience. The lead bohemian was titled after the great rock singer from the past “John Farnam” and when captured he was told – “This really is the last time”. That’s the kind of joke that flowed through the night and all of them went down extremely well. The music itself was very loud and very energetic. Unless you are an absolute die-hard, noone can match Freddy Mercury type of person you’ll appreciate the vocal talent that performed the extremely difficult songs Queen put together. Definitely worth seeing.

Just when you thought it was safe to turn the TV on again, Young Talent Time makes a come back. The worst part is that the Minogue sisters have promised to appear on the show – any hope that some actual talent may be found is lost…

I have slightly obscure tastes in music – particularly, I like musicals, not the highlights CDs the full recording of the original cast. It’s certainly not the most obscure taste in music but it does lead to an awful lot of trouble tracking down what I want and worse still I know what I want ahead of time unlike most people with really obscure tastes who just stumble across things they like. Coming back to the point though, you can’t just walk into HMV or pretty much any music store that I’ve found and pick up a copy of the original 1986 cast recording of The Phantom of The Opera or Miss Saigon or Les Miserables. However with this new fangled technology intarweb thingy I can head on over to Amazon and order it from there. There’s a bunch of other online stores around that may or may not have what I want for prices roughly equal to Amazon but what I love about Amazon is watching it try to predict my buying habits. I know most people freak out about privacy violations when computer systems start gathering data about them but with Amazon it’s like a fun game. It managed to pick that I was looking to purchase Miss Saigon and The Phantom Of The Opera the last time I went there and offered a package deal on them. It’s recommendations are also really quite good – including detecting that I tend to buy the versions that Lea Salonga is in (she tends to be part of the original cast of a lot of big musicals). Sadly, it doesn’t seem to have worked out that I only buy CDs from them as it keeps offering books and sheet music. While I do tend to buy a fair bit of sheet music of musicals I won’t purchase it without first flicking through it to make sure I have a chance of being able to play it. The big downside of buying from Amazon though is I have to wait two and a half weeks for things to arrive (that or pay an extra arm for postage).

Tor Norbye politely requests that the caps lock key be removed and the control key put there instead. There’s one very good reason why that shouldn’t be done: Everyone (except old school UNIX geeks) is used to the control key being where it is. Moving the control key would seriously annoy people. If you’re one of the people who are used to control being next to ‘a’ then imagine the whole world being as annoyed as you every time they use a computer and find that control is in the “wrong” place. More importantly though, putting control beside ‘a’ isn’t a good place anyway. The little finger is the most difficult finger to control on the human hand and is used least commonly. In touch typing, currently the left little finger is positioned over ‘a’ and moves up for ‘q’ and ‘z’. If you’re British or Australian, ‘q’ and ‘z’ are incredibly uncommon letters (American’s customi_z_ed their language by putting a bunch of Zs in). Now think of the most common keyboard shortcuts used on computers these days (think Windows users, not emacs users):

There seems to be a growing trend for projects to use XML configuration files – fine. There seems to be a growing trend for those projects to provide a schema for those files – good. There seems to be a growing trend for those projects never to validate their configuration files against the schema – bad. As I’ve previously mentioned, my job involves creating an XML forms editor and it turns out that this forms editor is really quite good at editing configuration files (see our very own configuration tool). We thought it might be nice to create a simple editor for Maven POM files. Sadly, it seems that the schema for a POM file doesn’t come anywhere near close to describing what should actually be in a POM. Maven has support for inheriting a POM and using the information in it, thus allowing that information to be omitted from the POM itself. Now admittedly, it’s not possible to specifically describe this in XML schema (the POM being inherited from can omit any information it likes as well assuming that it will be filled in by the extending POM), but the current schema insists that everything be specified in every POM file which makes validation completely useless. The POM files from the plugins don’t validate against the schema for a number of reasons as well. JDNC is even worse – Xerces finds errors in the schema itself (and I’m fairly sure Xerces is correct). This, combined with fairly poor documentation, makes it extremely difficult to implement tool support. It’s a shame, I’d probably use Maven if it wasn’t such a pain in the neck to create the POM file correctly (that and dependency management which is wonderfully simple for things in the public repository and annoyingly difficult for things that aren’t). Maybe I’ll come back and create a more useful schema for Maven at some point, but updating the schema doesn’t really help me identify the areas of our product that need improving.

Anton Tagunov added an excellent comment to yesterday’s entry:

The one thing that has always stopped me from doing this was: interning must use some global lock. So, while interning would cause little to no harm for desktop application it is likely to introduce extra synchronization bottleneck for server applications. Thus potentially degrading perfromance on some multi-cpu beast. Would you agree with this, Adrian? Firstly, let me make something very clear: string interning will cause bugs in your code and they will be hard to track down – they will however be easy to fix once found. At some point, someone, somewhere will forget to intern a string and let it pass into your code that assumes strings are interned. Also, string interning is an extremely situational optimization. In most cases, it will worsen performance because the overhead of interning the strings will not be made up for by the reduced complexity of comparisons. Even of the cases where it does help, most of the time the difference will not be noticeable. As always, don’t bother optimizing until you know that you need to and that it will help – this is an optimization that causes the code to become less maintainable. Having said that, lets go back to the original question. Firstly, does string interning require synchronization? Probably, but not in terms of Java. The String.intern() method is a native method and works via JNI. It would be difficult to imagine a way of achieving the behavior without at least some synchronization though. The synchronized block however would be very small, and very rarely encountered. There are two situations to consider, either the string is already in the interned list or the string is not. If it is, then no synchronization needs to occur because the list is only being read. So multiple strings can be interned at once so long as all of them are already in the interned list. Synchronization will be needed however whenever a string is interned for the first time (ie: it doesn’t match any String constant that has been loaded or any previously interned string). So on a multiple CPU system, it would be very bad to intern a lot of strings that are only ever used once or twice as they would require a lot of synchronization for no benefit. Of course on a single CPU system, doing this would be a bad thing anyway because it would incur the extra cost of comparing strings to check if they match an interned string without gaining any real benefit. My theory would then be (and only real world application profiling will confirm this in any particular situation) that the string interning technique is slightly less likely to pay off on multiple CPU systems, however because the situations in which string interning is useful require that the vast majority of String.intern() calls match something already in the cache (most likely one of the string constants they’re to be compared against) the question of how many CPUs will be in use isn’t going to have any significant impact. I can’t stress enough though that if you don’t have specific profiling data that shows String comparisons as the biggest bottle neck in your application, you shouldn’t apply this optimization. Great question. UPDATE: Here’s an interesting discussion of interning relating specifically to this question. The automatic google search on the side (if you actually click through to this blog entry) is very handy at times.

Elan Meng investigates the behaviours of string constants, interning and == compared to .equals. Very informative. The question remaining is, why would anyone ever use == instead of .equals on a String considering how likely it is to cause confusion and the potential for disaster if one of the strings for some reason isn’t interned. The answer is performance. In the average case, the performance difference between == and .equals is pretty much non-existent. The first thing .equals does (like any good equals method) is check if the objects are == and returns true immediately if they are. The second thing .equals does is check that the strings have the same length (in Java the length of the string is a constant field and so requires no computation). If an answer still hasn’t been found, the characters of each String are iterated over and as soon as they differ, false is returned. Now, consider the possible cases:

Angel Studios is starting to plan a round of screen tests for the people interested in being a part of our films and stage productions. We’d essentially like a database of actors we can flick through and find a list of people who might be suitable for a given role. We also need to do a bunch of auditions for our upcoming short film which is just starting production. There are a few people I want to get back in touch with to particularly invite along to do a screen test but we need to sort out exactly how we want to do it yet. Even so, if anyone’s interested in getting involved in film or stage productions, no experience is necessary, give me a yell (adrian at intencha dot com) and I’ll let you know when we’re actually ready to start doing some. It’s a lot of fun.

This is a great example of getting stuck in a mindset. A piece of very poorly written Java code is presented followed by a much shorter piece of Groovy code and Groovy is declared the winner.

The original Groovy:

list = ["Rod", "James", "Chris"]
shorts = list.findAll { it.size() <= 4 }
shorts.each { println it }

Java:

for ( String item : new String[] {"Rod", "James", "Chris" } )  if ( item.length() <= 4 ) System.out.println(item);

oooo, one line! It must be good… Of course if I were actually going to write that, I’d write it as: