Scoping refers to how software programs control which parts of the system can see which other parts. Back in the day, most things were global which meant that everything could see (and touch) everything else. This made writing the code easy, until you had a variable suddendly change out from under you. You then got to spend long hours finguring out who might have changed it...and you had to look everywhere because everyone had access.
Programming languages such as Java provide a number of scopes that can be specified to control who can see a particular variable. Ask the average Java programmer how many types of scope there are and they'll probably say three: public, private and protected. Public scope is like the old global...a public object can be seen and touched by anyone. Private scope is basically the opposite...a private object can only been seen by the class that owns it. Conventional wisdom says that most things should be private. Protected scope is a variation on private. A protected variable can be seen the class that owns it or by any class derived from that class.
Thats the answer you'll get from the average programmer, but its the wrong answer.
The right answer is that there are four scopes in Java. The scope that most people forget about is package scope. An object with package scope can be seen by any other object in the package. This is a surprisingly useful scope and so its a bit surprising that so many programmers ignore it. Part of the reason for that is that while the other three scopes each have keywords, you get package scope by not specifying any scope. Personally I think the language should have included a package_scope keyword so as to make this clear but thats water under the bridge.
Why is package scope so interesting?
Consider a software system with two classes: One and Two. Assume that we want to expose two methods to the outside world "begin()" and "end()". Further assume that each class needed to call a method in the other class. The following is the sort of code that most people would write.
package sample;
public class One {
public begin() {
new Two().internal();
}
public internal1() {
}
}
package sample;
public class Two {
public end() {
new One().internal1();
}
public internal2() {
}
}
Most people would tend to make the two internal methods public so that the two classes could use them. The problem with that is that it makes the two internal methods part of the publically accessible API of the overall system. A user of this package has no particular clue that they should or should not call those internal methods.
A better approach is to remove the "public" in the declaration of the two internal methods. This leaves them at package scope, which is just fine. The two classes are in the same package and so have access to all package scope methods. The two internal methods are now however absent from the publically visible API of the system, which is as it should be.
So, the rule of thumb should be:
default to making classes and methods package scope
make methods only used within a class private
and, only grudgingly make the hopefully small number of truely public methods be declared as public.
Your users and maintainers will thank you.
Tuesday, March 31, 2009
Monday, March 2, 2009
My JavaOne proposal was accepted!
My proposal to give a talk at JavaOne with my friend David Koelle was just accepted.
We'll be giving the following presentation in San Francisco in June.
Abstract: Would you like to create Java™ technology-based programs that play or create music but don't know where to begin? Come to this session to learn all about JFugue, an open-souce API that enables you to program music with ease. With its simple but powerful API, new UI components, and cool features, JFugue promotes creative music programming and exploration. For example, what if you could listen to what your application has been trying to say to you? Learn about Log4JFugue, which combines the power of Log4J and JFugue to turn your application's logging into a real-time song. By listening to your application, your pattern-matching brain can detect subtle changes in behavior that would normally be lost in a sea of log messages. The intended audience for this technical session is developers at any level who are interested in writing musical programs or who would like to use more parts of their brain to increase their productivity. In the session • Learn how to get and use JFugue • Learn about some advanced and exciting features of JFugue, including new ones • Learn about Log4JFugue for turning your log files into songs
We'll be giving the following presentation in San Francisco in June.
Abstract: Would you like to create Java™ technology-based programs that play or create music but don't know where to begin? Come to this session to learn all about JFugue, an open-souce API that enables you to program music with ease. With its simple but powerful API, new UI components, and cool features, JFugue promotes creative music programming and exploration. For example, what if you could listen to what your application has been trying to say to you? Learn about Log4JFugue, which combines the power of Log4J and JFugue to turn your application's logging into a real-time song. By listening to your application, your pattern-matching brain can detect subtle changes in behavior that would normally be lost in a sea of log messages. The intended audience for this technical session is developers at any level who are interested in writing musical programs or who would like to use more parts of their brain to increase their productivity. In the session • Learn how to get and use JFugue • Learn about some advanced and exciting features of JFugue, including new ones • Learn about Log4JFugue for turning your log files into songs
Monday, February 23, 2009
Re-experiencing content, followup
I've had several interesting conversations about re-experiencing content since the last post.
One friend asked about the phenomenon of people getting stuck on a particular content and watching / reading it over and over again. While this is usually associated with younger children who can watch the same episode of Thomas the Tank Engine multiple times a day, it sometimes occurs with adults as well. I think these are cases of the person looking for comfort through familiarity. When life seems unpredictable it can be comforting to revisit a content that won't surprise us. For small children most of life is unpredictable. Try to imagine how weird the world must seem before you figure out object permanence! I know that when I'm sick I'll tend to dig out an old movie to watch. This might also be why we watch certain movies (It’s a Wonderful Life) every year at a special time.
I’d distinguish this from watching a movie a few times to hear or memorize more lines, or to experience it again with the ending already known. I’ll confess to having watched some Monty Python movies too many times so as to memorize the lines from a scene or two. Inexplicably this is sometimes viewed as an accomplishment. :-)
Another reader wrote me to say: "These are very interesting matters. I haven't thought about them in an organized way before. I can watch a movie a few times (not multiple times, unless there's a lot of time in between). I've always supposed that the reason I want to listen to music over and over again is that I cannot really retain music--I mean I can remember short songs etc, but I can't unroll a whole symphony in my head, just parts of it, although musicians can replay the whole thing in their heads. I think I don't have the capacity. On the other hand, words stick in my head like glue. I have hundreds, maybe thousands, of word things, in my head but not a whole symphony or sonata. I remember songs, but probably because of the words. Do you think the content thing may have something to do with one's capacity for enjoying a particular medium? Some people are visual, verbal, or whatever? Interesting things to ponder"
Another person said that for them music could be re-experienced many times because they were different each time they heard the song. When it was pointed out that they were also different when they re-read a book they said that experiencing a book or movie was more immersive than listening to a song...there was less room for them. Perhaps listening to music is more of a participative thing while books / movies are more like being an observer? I don't necessarily share this belief but I can understand it. After all, I can listen to my ipod while coding at the office but they tend to frown on people watching movies there!
I wonder how this relates the concepts of Popular vs. Long Tail content? One school of thought says that most people will be watching the same small set of popular contents (the new “House” or “Heros” or “Battlestar”). The other school of thought says that most people will be off in their own corner watching their favorite old episode of “I Love Lucy”, “Hogan Heros”, or “F Troop”. For those of us designing Video Servers the difference matters. I’ve never heard the issue of whether individuals re-watch a given content brought up in the Popular vs. Long Tail discussions. Perhaps it should be.
One friend asked about the phenomenon of people getting stuck on a particular content and watching / reading it over and over again. While this is usually associated with younger children who can watch the same episode of Thomas the Tank Engine multiple times a day, it sometimes occurs with adults as well. I think these are cases of the person looking for comfort through familiarity. When life seems unpredictable it can be comforting to revisit a content that won't surprise us. For small children most of life is unpredictable. Try to imagine how weird the world must seem before you figure out object permanence! I know that when I'm sick I'll tend to dig out an old movie to watch. This might also be why we watch certain movies (It’s a Wonderful Life) every year at a special time.
I’d distinguish this from watching a movie a few times to hear or memorize more lines, or to experience it again with the ending already known. I’ll confess to having watched some Monty Python movies too many times so as to memorize the lines from a scene or two. Inexplicably this is sometimes viewed as an accomplishment. :-)
Another reader wrote me to say: "These are very interesting matters. I haven't thought about them in an organized way before. I can watch a movie a few times (not multiple times, unless there's a lot of time in between). I've always supposed that the reason I want to listen to music over and over again is that I cannot really retain music--I mean I can remember short songs etc, but I can't unroll a whole symphony in my head, just parts of it, although musicians can replay the whole thing in their heads. I think I don't have the capacity. On the other hand, words stick in my head like glue. I have hundreds, maybe thousands, of word things, in my head but not a whole symphony or sonata. I remember songs, but probably because of the words. Do you think the content thing may have something to do with one's capacity for enjoying a particular medium? Some people are visual, verbal, or whatever? Interesting things to ponder"
Another person said that for them music could be re-experienced many times because they were different each time they heard the song. When it was pointed out that they were also different when they re-read a book they said that experiencing a book or movie was more immersive than listening to a song...there was less room for them. Perhaps listening to music is more of a participative thing while books / movies are more like being an observer? I don't necessarily share this belief but I can understand it. After all, I can listen to my ipod while coding at the office but they tend to frown on people watching movies there!
I wonder how this relates the concepts of Popular vs. Long Tail content? One school of thought says that most people will be watching the same small set of popular contents (the new “House” or “Heros” or “Battlestar”). The other school of thought says that most people will be off in their own corner watching their favorite old episode of “I Love Lucy”, “Hogan Heros”, or “F Troop”. For those of us designing Video Servers the difference matters. I’ve never heard the issue of whether individuals re-watch a given content brought up in the Popular vs. Long Tail discussions. Perhaps it should be.
Sunday, February 15, 2009
The Kindle and the cost/payoff of experiencing content again
In thinking about the Kindle (Amazon's electronic book reader) I got thinking about a larger question about how people experience content. I'm one of those people who can watch the same movie multiple times, and I tend to accumulate tapes and DVDs of my favorite movies. My wife has never understood this, once she's seen a movie she's done with it and has no interest in seeing it again. We've both tended to think the other one was rather peculiar. We were at a brunch today and I tried to enlist support for my way of thinking but found surprising diversity.
Some people viewed movies as one-shot experiences but would read a book multiple times, others viewed both movies and books as one-shots, but most people viewed music as something to experience over and over again.
So I asked people: what's different about experiencing a song from experiencing a movie?
Several people said that while movies are based on a narrative, they did not see music that way. Several said that they did not feel that songs told a story (some of the others of us found that idea shocking...of course a song tells a story...for us). So for these people a movie is boring the second time around because the know the story but a song is just an experience ... so repeating it is still rewarding...perhaps like eating ice cream? The fact that you've eaten ice cream before doesn't diminish your enjoyment of more ice cream.
I wonder if there is a different kind of answer underlying this: limited time. I can listen to a song in 2-3 minutes, watching a movie takes about two hours, and reading book might take 5-10 hours. Who has that kind of time for a repeat?
On the other hand, there is a payoff for getting involved in a long story...you get to know the characters. I tend to dislike short stories because why should I get invest time in a story that won't return my investment? Think of the angst many people feel when a beloved TV series ends (The Sopranos, Friends, Mash, etc). There has been an investment and the end of the story brings an end to the return on that investment. For some of us, re-watching a movie gives us some extra return on the time we spent on the content in the first place.
The link back to the Kindle for me is that for many people the fact that Kindle does not contain your existing library of books is simply not an issue. Many people view their existing library of books as more or less dead storage; perhaps to be rarely accessed at some time but certainly not in need of ready access. From this point of view loading the Kindle with only new material is just fine. I suspect that this sort of person would also be happy with a Kindle-like device with very limited storage, perhaps only enough to hold the books you were currently reading.
Some people viewed movies as one-shot experiences but would read a book multiple times, others viewed both movies and books as one-shots, but most people viewed music as something to experience over and over again.
So I asked people: what's different about experiencing a song from experiencing a movie?
Several people said that while movies are based on a narrative, they did not see music that way. Several said that they did not feel that songs told a story (some of the others of us found that idea shocking...of course a song tells a story...for us). So for these people a movie is boring the second time around because the know the story but a song is just an experience ... so repeating it is still rewarding...perhaps like eating ice cream? The fact that you've eaten ice cream before doesn't diminish your enjoyment of more ice cream.
I wonder if there is a different kind of answer underlying this: limited time. I can listen to a song in 2-3 minutes, watching a movie takes about two hours, and reading book might take 5-10 hours. Who has that kind of time for a repeat?
On the other hand, there is a payoff for getting involved in a long story...you get to know the characters. I tend to dislike short stories because why should I get invest time in a story that won't return my investment? Think of the angst many people feel when a beloved TV series ends (The Sopranos, Friends, Mash, etc). There has been an investment and the end of the story brings an end to the return on that investment. For some of us, re-watching a movie gives us some extra return on the time we spent on the content in the first place.
The link back to the Kindle for me is that for many people the fact that Kindle does not contain your existing library of books is simply not an issue. Many people view their existing library of books as more or less dead storage; perhaps to be rarely accessed at some time but certainly not in need of ready access. From this point of view loading the Kindle with only new material is just fine. I suspect that this sort of person would also be happy with a Kindle-like device with very limited storage, perhaps only enough to hold the books you were currently reading.
Saturday, January 24, 2009
How Digital Cameras remind me of the old B&W days
Recently my Tai Chi instructor asked me to take pictures of my class for the school's web site. His digital camera has some shutter lag which makes photographing people in motion a hit or miss proposition. So, I took a hundred or more shots, knowing that I only needed a couple of good shoots.
As I was doing this I was reminded of my old days learning to shoot black and white photos, (which happened long before there was such a thing as digital photography) and I was struck by the similarities.
I learned photography from an old friend, long since passed away named Christopher Resnik. Chris taught photography from the ground up. We bought 100 foot rolls of 35mm film and made our own film cartridges. Cameras back then were fully manual and Chris wouldn't even let us use a light meter...preferring to train our eyes to read the light and determine the exposure. To this day I can look around and know that such and such a day requires an F8, 1/250 second exposure with 400 ASA film. Today most people probably don't even know what those terms mean.
Since we bought film in bulk and did all of our own darkroom work it was quite inexpensive and so we shoot a lot. Chris used to say that is you got one or two good shots out of a 36 exposure roll you were doing well. When we found an interesting subject we'd take a number of shots of us...from various angles, with various exposures and with various perspectives. We might take whole roll of film on a single subject. Taking 100 Tai Chi shots reminded me of that.
Back in the days before digital cameras a roll of color film might cost $3-$5 to buy and then perhaps $10-$12 to process. With that price model you were careful how you spent your photos and a roll of film might sit in the camera for months or a year.
We've now come full circle in a way. Photos are basically free, especially since many people never make prints but instead view their photos on a digital picture frame or online via Snapfish or KodakGallery.
A missing element for most digital photographers however is the culling process. Back in the day, after processing a roll we'd stay in the darkroom evaluating our photos and would throw out 90% of them. We shot 36 pictures of that flower so that we could find the best one, but then we left the other 35 shots on the darkroom floor. Today most digital photographers take the 36 photos, post them all to Snapfish and go on their way. After a few months they have 100s or 1000s of pictures, most of which are awful and have no idea where the dozen or so gems are.
I'm sure there's a metaphor in here for the pace of modern life but it escapes me. I do however like when life comes full circle.
For my own pictures, (and I have a 3 year son so I take a lot of pictures), I've developed a culling process. When I plug my digital camera or my IPhone into the computer it creates a new directory where all the pictures go. I then create a subdirectory called so_so_shots. I immediately look at each picture and if it isn't great it gets moved to the so_so_shots directory. Since I'm just moving them rather than deleting them I can be quick and ruthless in the decision. This lets me easily manage a much smaller set of much better pictures.
As I was doing this I was reminded of my old days learning to shoot black and white photos, (which happened long before there was such a thing as digital photography) and I was struck by the similarities.
I learned photography from an old friend, long since passed away named Christopher Resnik. Chris taught photography from the ground up. We bought 100 foot rolls of 35mm film and made our own film cartridges. Cameras back then were fully manual and Chris wouldn't even let us use a light meter...preferring to train our eyes to read the light and determine the exposure. To this day I can look around and know that such and such a day requires an F8, 1/250 second exposure with 400 ASA film. Today most people probably don't even know what those terms mean.
Since we bought film in bulk and did all of our own darkroom work it was quite inexpensive and so we shoot a lot. Chris used to say that is you got one or two good shots out of a 36 exposure roll you were doing well. When we found an interesting subject we'd take a number of shots of us...from various angles, with various exposures and with various perspectives. We might take whole roll of film on a single subject. Taking 100 Tai Chi shots reminded me of that.
Back in the days before digital cameras a roll of color film might cost $3-$5 to buy and then perhaps $10-$12 to process. With that price model you were careful how you spent your photos and a roll of film might sit in the camera for months or a year.
We've now come full circle in a way. Photos are basically free, especially since many people never make prints but instead view their photos on a digital picture frame or online via Snapfish or KodakGallery.
A missing element for most digital photographers however is the culling process. Back in the day, after processing a roll we'd stay in the darkroom evaluating our photos and would throw out 90% of them. We shot 36 pictures of that flower so that we could find the best one, but then we left the other 35 shots on the darkroom floor. Today most digital photographers take the 36 photos, post them all to Snapfish and go on their way. After a few months they have 100s or 1000s of pictures, most of which are awful and have no idea where the dozen or so gems are.
I'm sure there's a metaphor in here for the pace of modern life but it escapes me. I do however like when life comes full circle.
For my own pictures, (and I have a 3 year son so I take a lot of pictures), I've developed a culling process. When I plug my digital camera or my IPhone into the computer it creates a new directory where all the pictures go. I then create a subdirectory called so_so_shots. I immediately look at each picture and if it isn't great it gets moved to the so_so_shots directory. Since I'm just moving them rather than deleting them I can be quick and ruthless in the decision. This lets me easily manage a much smaller set of much better pictures.
Tuesday, January 20, 2009
Why I don't want a Kindle yet
The Kindle is Amazon's book reader and its an amazing device, but one that I don't want yet.
The Kindle has an astonishingly readable screen (using electronic ink rather than a display tube or LCD). This means that once its painted a page there is no electricity needed to maintain the image so its always on, and the battery life is very good.
So why don't I want one of these cool devices that would let me take all/most of my books with me? Because Amazon wants me to pay for all of those books again.
As I look at my book shelves I see hundreds of books, most which were purchased from Amazon. They know this. And yet, when I buy a Kindle I have to turn around and repurchase all of those books again if I want to put them on the device. And I have to pay what amounts to full price.
When you buy a Kindle Amazon should give you and electronic copy of all they books you've purchased from them, say in the last couple of years. Until they do something like that the advertising line that you can take all your books with you simply isn't meaningful.
The Kindle has an astonishingly readable screen (using electronic ink rather than a display tube or LCD). This means that once its painted a page there is no electricity needed to maintain the image so its always on, and the battery life is very good.
So why don't I want one of these cool devices that would let me take all/most of my books with me? Because Amazon wants me to pay for all of those books again.
As I look at my book shelves I see hundreds of books, most which were purchased from Amazon. They know this. And yet, when I buy a Kindle I have to turn around and repurchase all of those books again if I want to put them on the device. And I have to pay what amounts to full price.
When you buy a Kindle Amazon should give you and electronic copy of all they books you've purchased from them, say in the last couple of years. Until they do something like that the advertising line that you can take all your books with you simply isn't meaningful.
Thursday, January 8, 2009
A Tutorial for Adding Groovy to a Java Project
I program primarily in Java and have done so for close to ten years. Before that I programed in C++, C, Pascal, Prolog (yes, I had a real job using Prolog!), and even Fortran and assembler. So I know that languages wax and wane in their importance. So, I decided to add a class or two written in the Groovy language to one of my side projects.
For those not familiar with Groovy its one of a surprisingly large group of languages whose source code is different from Java, and yet runs on the Java runtime. Java source code is compiled into Java bytecode which is executed by the Java Virtual Machine (JVM) on your computer. Groovy source code is also compiled into Java bytecode which then runs on the very same JVM. This allows the two languages to interoperate in interesting ways.
As a starting point for this tutorial I assume you have an existing Java based project, use Ant to build your system and use Eclipse as your development environment. None of that is required for Groovy but it is a fairly standard setup and its what I use, both at home and at work.
The steps are basically
a) download and install the Groovy GDK
b) add a how-to-compile-groovy task to your Ant build.xml (the task is included in the GDK)
c) add the groovy-all.jar file to your library path
d) add the groovy-plugin to your Eclipse project
e) enable groovy-nature in your Eclipse project
f) write a Groovy class and use it.
Overall this should take no more than twenty minutes or so. One of the really cool things is that once you have a Groovy class you can use it from your Java classes just like any other class...your Java code has no idea its using a class written in Groovy.
Now lets look at the steps listed above in cookbook manner.
a) go to http://groovy.codehaus.org/Download and select the latest stable release (currently 1.5.7). Click on the download link and follow the very simple instructions.
b) add the following task to your build.xml to define how to compile groovy code:You then need to actually compile your groovy source files. A standard build.xml will have a compile target that invokes the javac task compile your java source files. I changed that so the my compile task was empty but depended on java_compile and groovy_compile targets. See the full definition of the groovyc task options here: http://groovy.codehaus.org/The+groovyc+Ant+Task
c) the Groovy GDK includes a groovy-1.5.7-all.jar file. Add this to your library and execute paths
d) From Eclipse, select Help, Software Updates, Find and Install, Search for new features to install, next.Now select New Remote Site. Enter Groovy as the Name and http://dist.codehaus.org/groovy/distributions/update as the URL.Press Ok and you should find Groovy added to the list of Sites to include in search. Press Finish.It should find Groovy, check the features you want and press Next.Accept the license terms and press Finish. At this point the plugin will be downloaded and installed.
e) From Eclipse select your proejct, right click and select Groovy->Add Groovy Nature. Eclipse will now understand files with the .groovy extension.
f) Remember that any Java file is also a Groovy file, so if you want to start with baby steps just rename one of your java files to have a groovy extension. Eclipse and Ant will recognize it and compile it to bytecode and then allow you to use it.
You could then take another small step and remove most of the semi-colons, because Groovy doesn't require them.If your class has import statements from various java packages you can probably remove them as well since Groovy automatically imports them.
Clearly you then want to write a class that actually uses Groovy features but that's beyond the scope of HelloGroovyInAJavaProjectWorld.
Enjoy.
For those not familiar with Groovy its one of a surprisingly large group of languages whose source code is different from Java, and yet runs on the Java runtime. Java source code is compiled into Java bytecode which is executed by the Java Virtual Machine (JVM) on your computer. Groovy source code is also compiled into Java bytecode which then runs on the very same JVM. This allows the two languages to interoperate in interesting ways.
As a starting point for this tutorial I assume you have an existing Java based project, use Ant to build your system and use Eclipse as your development environment. None of that is required for Groovy but it is a fairly standard setup and its what I use, both at home and at work.
The steps are basically
a) download and install the Groovy GDK
b) add a how-to-compile-groovy task to your Ant build.xml (the task is included in the GDK)
c) add the groovy-all.jar file to your library path
d) add the groovy-plugin to your Eclipse project
e) enable groovy-nature in your Eclipse project
f) write a Groovy class and use it.
Overall this should take no more than twenty minutes or so. One of the really cool things is that once you have a Groovy class you can use it from your Java classes just like any other class...your Java code has no idea its using a class written in Groovy.
Now lets look at the steps listed above in cookbook manner.
a) go to http://groovy.codehaus.org/Download and select the latest stable release (currently 1.5.7). Click on the download link and follow the very simple instructions.
b) add the following task to your build.xml to define how to compile groovy code:
c) the Groovy GDK includes a groovy-1.5.7-all.jar file. Add this to your library and execute paths
d) From Eclipse, select Help, Software Updates, Find and Install, Search for new features to install, next.Now select New Remote Site. Enter Groovy as the Name and http://dist.codehaus.org/groovy/distributions/update as the URL.Press Ok and you should find Groovy added to the list of Sites to include in search. Press Finish.It should find Groovy, check the features you want and press Next.Accept the license terms and press Finish. At this point the plugin will be downloaded and installed.
e) From Eclipse select your proejct, right click and select Groovy->Add Groovy Nature. Eclipse will now understand files with the .groovy extension.
f) Remember that any Java file is also a Groovy file, so if you want to start with baby steps just rename one of your java files to have a groovy extension. Eclipse and Ant will recognize it and compile it to bytecode and then allow you to use it.
You could then take another small step and remove most of the semi-colons, because Groovy doesn't require them.If your class has import statements from various java packages you can probably remove them as well since Groovy automatically imports them.
Clearly you then want to write a class that actually uses Groovy features but that's beyond the scope of HelloGroovyInAJavaProjectWorld.
Enjoy.
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