Are Design Patterns How Languages Evolve?

Here's an interesting post. I had sort of mentioned a little about this in a previous post long back. Any thoughts?

Re: Integrating OpenEJB with Tomcat 5.0

I know what you guys are thinking - "Dinesh talking about EJB


Welcome to the Dark Side!! Btw how many of you all like Star Wars??



I guess you all know that Tomcat is not an EJB Container and as such requires external support for it to work with EJB's, well I at work have been reading on EJB's for the past few days and as usual being my impatient self, just couldn't contend myself with reading the book, I had to see and run some code. Well, I already had Tomcat installed so I was wondering if there's anything I can do to get it working with EJB's and that's when I fell upon OpenEJB. (I think there's also Jboss)


I'll just give a brief intro. Tomcat is a J2EE Web Container which can be used to deploy Java Server Pages(JSP) and Servlets both of which are used to create dynamic web pages. Open EJB is (i suppose) just an EJB Container which allows you to deploy EJB's. OpenEJB and JBoss are open source implementations.



Revo, you'll really love this, that's if you already haven't done it. Just try it out, it's really simple and yet so powerful.


You mean calling EJB's from JSP's or Integrating OpenEJB and Tomcat?

I have used Sun's Reference Implementation(RI) J2EE App Server for deploying my EJB's. The RI includes Tomcat as a Web Container so you do not have to manually integrate. Also the RI has a good admin console. The RI is free for use. I am not sure about the source. I haven't used OpenEJB. I guess the RI will be more user friendly.



It was a great moment to see my SessionBean being called from my jsp. A good experience, but yet I'd rather be writing cryptic C++ code ;)


I am sure you have read about the functionality provided by J2EE App Servers.. all the distibuted stuff.. implicit middleware etc. Writing an app to achieve functionality like this will really take a huge team and loads of cryptic code. Btw are there any C++ App Servers which provide such services??


Also I spoke of the Dark side. EJB's are difficult to use. Don't Make me Eat the Elephant Again is an article that talks a bit on what the situation is today. There are alternatives to EJB like Spring + Hibernate which I have been hearing a lot of but have never had time to read about. Also the EJB 3 release will be coming soon which is based on J2SE 5.0 and heavily uses annotations which should really simplify coding.

Mohn.. could you mention a little about how the .NET framework handles persistence for the Enterprise?? I have heard that it is simple compared to the Java model.

Re: Adventures with Linux

Looking around I came across ndiswrapper on sourceforge. This is a really neat project which uses windows drivers to get linux to recognize the card. I had some trouble with the newest vesion (1.1), so tried different versions (.10, .09), compiled and can it. It worked! So configured "wlan0" and now writing this post in Opera 8.0 on Mandrake 10.0! Just had a feeling of euphoria!


Woohooo... Congrats man on finally getting your wlan working. Mohn had asked me to help with ndiswrapper ages back.. and as lazy as I am, he had to do it himself!!



You would think that having struggled with it for so long, I would be quite sick of it. In some ways I am, but I've also learnt a lot in the process. And this is the essence of Linux.


Exactly. There are so many things we just take for granted when we use Windows. But only for customization etc when you go deep into Linux do you understand a lot more about the OS and other stuff.

SciTE Text & Code Editor

I have to admit that I'm a Editor freak!! I keep scourging the net for free, fast and good text editors namely for the Windows Platform. On Linux, Vim just kicks everyone else's butt!!

Recently I came across SciTE which in my opinion is one of the best I have ever used. It's simple and extremely fast. It's also extremely customizable and supports an array of programming languages!!

I think I'm going to stick with this editor for quite some time, hope you guys check it out!

Dinesh.

Integrating OpenEJB with Tomcat 5.0

I know what you guys are thinking - "Dinesh talking about EJB, GIVE ME A
BREAK!!" ;) But as the Walrus said "The time has come to talk of many
things" :)

I guess you all know that Tomcat is not an EJB Container and as such
requires external support for it to work with EJB's, well I at work have
been reading on EJB's for the past few days and as usual being my
impatient self, just couldn't contend myself with reading the book, I
had to see and run some code. Well, I already had Tomcat installed so I
was wondering if there's anything I can do to get it working with EJB's
and that's when I fell upon OpenEJB. (I think there's also Jboss)

I will not go into what you should do inorder to integrate the two cause
there's already an excellent article available on the subject at OnJava.com.

Revo, you'll really love this, that's if you already haven't done it.
Just try it out, it's really simple and yet so powerful.

It was a great moment to see my SessionBean being called from my jsp. A
good experience, but yet I'd rather be writing cryptic C++ code ;)
(Sorry, I'll be me, always!)

Dinesh.

Adventures with Linux

Ok, I admit it. I've been a blind bastard. Blind to Linux and open source. I've read about it and been keeping up with what's been going on in the "community" but never really "got" it. Well, I think something finally hit me - that light bulb turned on. Anyway, I've decided to write some stuff about my Linux experience.

Here's a brief history of my dealings with Linux as a total newbie (warning: boring stuff ahead). What got me interested in Linux, was my India trip in summer 03 when Rahul and Hrishi were using it. Before that, I never really thought about trying it out and didn't have much interest in it. But the way they spoke about it, I couldn't resist having a go at it. So after coming back, I installed Red Hat 9 on a couple of machines. At the time, I had a network setup over the phoneline and wasn't able to get Red Hat to recognize the NIC. Basically I gave up after several futile posts to message boards and many email exchanges with Rahul. Last May, I installed Mandrake 10 in the hopes that it would work. No luck there either. I realize it was my network setup - which was quite rare. So I gave up on that too. Last summer, I changed over to a wireless network. This time, I was a little more hopeful because this was a more common network setup. Anyhow, long story short, I had a usb wireless adaptor and Mandrake didn't recognize it. I remember spending an interesting afternoon with Rahul on messenger giving me step by step instrutions to recompile the kernel with added support for wireless drivers. Unfortunately, didn't work. Also tried Knoppix without luck. Finally, I installed Mandrake on a laptop which had a wirless card built in. This was pcmcia so I was hoping for better. Again, no luck.

Looking around I came across ndiswrapper on sourceforge. This is a really neat project which uses windows drivers to get linux to recognize the card. I had some trouble with the newest vesion (1.1), so tried different versions (.10, .09), compiled and can it. It worked! So configured "wlan0" and now writing this post in Opera 8.0 on Mandrake 10.0! Just had a feeling of euphoria!

You would think that having struggled with it for so long, I would be quite sick of it. In some ways I am, but I've also learnt a lot in the process. And this is the essence of Linux.

I'll post some stuff about some stuff I've liked about Linux next time.

RE: Stroustrup's Interview Leaked...

The "matter" is obviously a bunch of ******* bullshit but I would have liked to believe that it was Bjarne's idea of a joke! :-p

RE: Stroustrup's Interview Leaked...

I second Dinesh's "you got to be kidding right?" comment. Obviously the work of a C programmer.

RE: Stroustrup's Interview Leaked...

You actually thought that it was Bjarne Stroustrup?? You got to be kidding, right??

Dinesh.

Stroustrup's Interview Leaked...

I don't know how far this is true but entertaining to read nevertheless... :-)

Here's the link.

Implementing "finally"

Java has this great facility when dealing with exceptions called "finally". When you have a finally block, any code within it will execute regardless of whether an exception has been thrown or not. It's a good place to put code that must absolutely positively be run like closing files, database connections and any other similar resources. C# also has it and I believe it's also been standardized in C++, but not sure. Anyway, ever wonder how it is actually implemented?

I wrote a really simple method that just has a try, catch, finally block and examined the bytecode generated using this really cool Eclipse plug-in.

Here's the java code...

public void testFinally()
{
    try
    {
        System.out.println( "try" );
    }
    catch ( Exception ex )
    {
        System.out.println( "catch" );
    }
    finally
    {
        System.out.println( "finally" );
    }
}

and here's the bytecode...

// testFinally()V
L0 (7)
GETSTATIC java/lang/System.out: Ljava/io/PrintStream;
LDC "try"
INVOKEVIRTUAL java/io/PrintStream.println(Ljava/lang/String;)V
GOTO L1
L2 (9)
ASTORE 1
L3 (11)
GETSTATIC java/lang/System.out: Ljava/io/PrintStream;
LDC "catch"
INVOKEVIRTUAL java/io/PrintStream.println(Ljava/lang/String;)V
L4
GOTO L1
L5 (14)
ASTORE 3
JSR L6
ALOAD 3
ATHROW
L6
ASTORE 2
L7 (15)
GETSTATIC java/lang/System.out: Ljava/io/PrintStream;
LDC "finally"
INVOKEVIRTUAL java/io/PrintStream.println(Ljava/lang/String;)V
L8 (16)
RET 2
L1 (14)
JSR L6
L9 (17)
RETURN
L10
LOCALVARIABLE this Ltest; L0 L10 0
LOCALVARIABLE ex Ljava/lang/Exception; L3 L4 1
MAXSTACK = 2
MAXLOCALS = 4

I don't understand bytecode. I would be interested in knowing more about it. But anyway, you don't need to be a bytecode specialist to understand how "finally" is always executed regardless of exception or not...

This is the "try" part

L0 (7)
GETSTATIC java/lang/System.out: Ljava/io/PrintStream;
LDC "try"
INVOKEVIRTUAL java/io/PrintStream.println(Ljava/lang/String;)V
GOTO L1

and this is the "catch" part

L3 (11)
GETSTATIC java/lang/System.out: Ljava/io/PrintStream;
LDC "catch"
INVOKEVIRTUAL java/io/PrintStream.println(Ljava/lang/String;)V
L4
GOTO L1

Notice any similarities? What is at "L1"?

L1 (14)
JSR L6

JSR is a jump instruction. So all this does is just to location L6. As you would suspect, it is the finally block...

L6
ASTORE 2
L7 (15)
GETSTATIC java/lang/System.out: Ljava/io/PrintStream;
LDC "finally"
INVOKEVIRTUAL java/io/PrintStream.println(Ljava/lang/String;)V

Voila. Mystery solved!

I have to say that the bytecode is NOT the most diffcult thing in the world to interpret. A lot of it is pretty self-explanatory. I realize this is a real toy example and it gets more complicated, but it looks like something one can pick up. It's the same situation with IL code in the .NET world. I think maybe IL is a bit easier to read.

Maybe not the most important thing, but something that's interesting and nice to know.

The essential Java language library

The essential Java language library

Seems like a decent list. Of the books mentioned, I can vouch for "Effective Java". Haven't read Bruce Eckel's "Thinking in Java", but he's a good writer... "Thinking in C++" was a good read and we've included him in many of our discussions! And I know Rahul is a big fan of "Design Patterns". As far as sites are concerned, onjava.com and theserverside.com have decent articles. onjava.com is part of oreilly which I really respect.

What are some of your fav books? We discussed books we'd LIKE to read long back, but what about books you've already read? I'll mention three - "Applied .NET Framework Programming", "Effective Java" and "The C++ Object Model". I really like books that go into detail and explain HOW things work, you know what's going on underneath the covers or talk about best practices rather than just talk about syntax. I think all these three do that and more.

Java turns 10

See James Gosling (and friends) celebrate his kid turning 10.

Warning - celebration is pretty pathetic.

Re: More on Mono

UML and strict development is good, but it's important not to get caught up in it. While I agree with their usefulness in practical situations, one must always remember that the final aim to churn up good code - and good software CAN be designed and implemented using basic common sense and just applying your mind to the problem and breaking it up into smaller parts.

When you try to make something too systematic, you run the risk of unnecessarily complicating matters. It's for us to decide where to draw the line. Use the 'formal' tools on a broad level but don't limit yourself to those or try to adhere to them like they're sacrosanct. Keep the big picture in mind and let creativity gain the upper hand! At the same time, you can't just 'hack' your way through in large apps. It's for the individual to optimize based on his requirements.

As far as mono goes, I don't have experience with it but based on whatever little I've read/heard about it, here's my two cents anyway! I don't have a great feeling about mono. It might pick up, you never know but if I were to develop a software, I wouldn't use mono! It's hard to give precise reasons; it's just a general feeling you get.

Re: More on Mono

Firstly, seems like I struck a nerve. Seriously didn't mean to offend.

Everything you said is valid. No doubt. I was just trying to say that it really seems like things tend to become quite complicated. As you said UML is a recognized standard for communicating but it isn't required in every situation. UML is something that has come up with OOP. What about developers not using OOP? Correct me if I'm wrong, but most Linux/open source projects are still done in lower level, non-OO languages, primarily C. Many of these projects are quite huge and the ideas need to get across to many developers. How are they able to do it?

I have not downloaded or worked on any open source projects, even ones based on .NET or Java at places like sourceforge.net, but I wouldn't be surprised if there were no UML diagrams available with the source at these places. I suppose there are tools that will generate these diagrams automatically for you from source. VS .NET 2005 has this capability. I believe there are plug-ins for Eclipse also.

And what about Scripting. I've mentioned over a few posts about its gaining popularity. They are shedding their "toy" status and are being used in larger projects too. A lot of them are OO oriented, but not in the strict sense as in Java and .NET. So again, I wouldn't think UML is very popular in those communities.

I probably threw one too many things in the same boat by including Design Patterns in my dumb rant. I have'nt read the book you mentioned. I should, before saying more. I've primarily referred to this site. It seems to have most, if not all, the major ones listed. As an interesting point, I feel design patterns will be added into languages. For example, the Observer pattern is already a built in component of .NET with Delegates and Events. The next version will include a way to create a "static" class, wherein you can't create an instance of it - i.e. Singleton. If you think about it even getters/setters are in a way design patterns and they are built into .NET languages.

I'm digressing quite a bit, but this is just an example of what I'm talking about. I know I'm taking it out of context... I'm only talking small projects. But can't help but think that the trend is towards more complexity even though things like XP are trying to put up some resistance.

As an aside, dyou understand how open source projects work? How are so many people able to work on a project "unsupervised" as it were? Somehow it's just hard to imagine.

Personally I am very skeptical of Mono being used widely.

I'm assuming this is because of it being tied to .NET. Do you feel Linux guys will always reject it because of the "connection" to MS, even though it might be something useful?

Re: More on Mono

One of the questions in the interview was about the development process behind Mono. He gives a really good answer about not being a great fan of UML and strict development processes. They are all great hackers and just want to do it because they are having fun... enjoying it. Strict dev practices etc... limit creativity and the "art" of programming.

What dyou think of his answer? I want to learn good practices about developing software because right now we all lack any substantial experience with it. But at the same time, I read about UML, design patterns, agile development, "some new hyped up buzzword" etc... and it all just seems so "messy" or tends to complicate matters. Same feeling I have with some Java developments. I've mentioned them before. It feels a lot of over engineering.


UML is a diagrammic notation to express Software design at various stages of development. You should learn UML because it is the de-facto method for communication between dev's. So if I show you a UML Class diagram you immediately know what inherits what and methods etc.. blah blah. As I mentioned various stages of developement exist for a particular piece of software. In the initial stage a Use Case diagram is made, then Analysis diagrams, then Design diags. All these help in development.

Now there are many methodologies for developing software. The various stages I mentioned were wrt the Waterfall process (or the Unified Dev Process), which I must admit is very boring. Too much documentation and managerial in nature. But understandably in a large organisation these things become important. Other methodologies include the Agile process. Agile process includes XP development practices which seem more Developer friendly. Many methodologies or processes use UML diagrams to express artifacts (or products) at various stages of development.

So firstly you should learn UML diagrams. Reading about various Development processes is also good. You will get an idea as to how many co's work. Dinesh could probably tell us a bit about his company. Which process you apply is a different matter.

And Design Patterns is a separate issue altogether. Which book for patterns or articles have you read?? Design Patterns was the first book to talk about patterns and is simply put a Bible. I have had the book since a while and even suggested to you guys to read the book. But to be frank I have not been able to understand too many patterns. We did try to apply a few in the Object Oriented Analysis and Design Module here at Ncb. Recently I read a sample from this book from Oreilly Head First Design Patterns. Read the sample chapter. The style of the book is very different, and I really loved it. Only after you read a few design patterns do you realise how beautiful solutions to generic problems can be !!

And complications in Java is another issue. I'll talk about Java some other time. I think you have mixed too many questions in one paragraph. Read about stuff to get an idea of things. UML and Design Pattens should be high on the priority list.


Also, any opinions about Mono? From his blog sometime back - "7 out of the 20 top-rated apps on gnomefiles.org are mono apps".


Even since coming here to Ncb I have harldy booted into Gentoo, and am not aware of whats going on in the Linux world. Probably Hrishi could shed more light on the popularity of Mono apps. Personally I am very skeptical of Mono being used widely.

More on Mono

Kinda obvious, but one of the great things about the programming world is that you interact, learn from, help and work with people from all over the world. Here's a video from Turkey interviewing Miguel De Icaza - the Mono dude (also GNOME founder). Can't understand half the things the interviewers are saying. I thought they were talking Turkish... turns out it was English.

Anyway, I really got a lot of respsect for Miguel. His blog gives you a good insight into his views - and not just programming related. He's like a really experienced open source hacker. Just feel like if you worked under him you would learn a lot. One of the questions in the interview was about the development process behind Mono. He gives a really good answer about not being a great fan of UML and strict development processes. They are all great hackers and just want to do it because they are having fun... enjoying it. Strict dev practices etc... limit creativity and the "art" of programming.

What dyou think of his answer? I want to learn good practices about developing software because right now we all lack any substantial experience with it. But at the same time, I read about UML, design patterns, agile development, "some new hyped up buzzword" etc... and it all just seems so "messy" or tends to complicate matters. Same feeling I have with some Java developments. I've mentioned them before. It feels a lot of over engineering. Granted this is coming from someone with little experience, but haven't you read an article which goes on about something and at the end of the 20th page you think, what the hell was that? Just seems so complicated for something which could have been done more simply.

Also, any opinions about Mono? From his blog sometime back - "7 out of the 20 top-rated apps on gnomefiles.org are mono apps". I was quite surprised/impressed. It looks like it's use has picked up.

Google: Behind the scenes

Streaming vid (~1 hr): Behind the scenes at Google

One (more) thing which is impressive is they've built their services on top of commodity hardware... no super expensive machines. Just regular stuff with a lot of redundancy. Also, they have a ton of in built stuff - from a Google File System to some map/reduce algorithm which is infrastructure code to be fault tolerant and distribute the load among different machines (mentioned in the talk). They've recently started to share some of this.

Re: Databases Part 1

Waiting on part deux.

You'll have to wait for some more time... Very busy with the current module at Ncb as reaching the submission deadline.


A table can have a primary key.

When you say "can" dyou mean a primary key is NOT necessary? I thought it would be.


Right. A primary key is NOT necessary. But searching for a particular row will be more complicated as duplicates can be added to the table.


One thing that needs to be considered is where the error checking happen? Does it happen in the "business logic" layer or directly in the data layer? I would think a lot of times the database should ONLY be conserned with storing information.

I guess the question comes down to what responsibilities the database should take on. It seems the trend is to make more and more things happen in the data layer.


Basically databases are becoming more intelligent. So more Business logic is being pushed into the databases. It seems like mixing of responsibilities, but only specific business logic could be put into the db. Like you need to retrieve some data occasionally which spans across many tables and this is done very often. Rather than have loads of SQL in your business logic, just call a stored proc.

Another trend is distributed databases, which still have to mature well.

Error handling is possible in Stored procs. But I am not very sure how errors are sent to the host language. I think a simple SQLError could be returned by the db. We returned C-style status codes from the Stored procs.


Each trigger is associated with a TABLE on some event.

This is quite cool. I didn't know this was possible. You can basically keep a log/trace of everything that's going on in your database this way.


Care has to be taken that triggers are not written on 'events' of heavily used tables. Events could be insert, delete. Now if I have 500 inserts per sec on a table and I write a trigger on that event, its going to really load the server.


I'm interested in Stored Procedures just because I've read that they are beneficial to app performance. Is that really true?


Yes its true.

Now for some explanation.

When a simple query is submitted to a database, a few steps are carried out after which the result is returned. These include checking if the query is valid and tries to reference valid tables and columns. Then optimization of the query is done. Most queries in SQL are commutative and associative, so the order of the operations in the query can be changed without changing the meaning of the query as a whole. So the db does this based on the information it has about its tables and some heuristics as well. After this, the new SQL query tree is compiled and finally executed to return a result. Now as you have noticed, this is a very complicated and lengthy process. (and trust me, db's are really smart already wrt optimization!!)

Back to Java. There are three ways to execute a query in Java SQL - A Statement, a PreparedStatement and a Callable statement.

Now in a simple statement, the query is sent from the host language, then goes through all the steps of checking and optimization mentioned above.

A prepared statement is cached into the db for some time. So it does not have to go through all the optimizations steps each time. Probably only the new arguments have to be checked which should be faster.

A Callable statement is used to run a Stored Procedure. Now a stored procedure query resides IN the db. Only arguments are passed similar to a Prepared statement. So all optimization, compilation is already done.

I guess that should explain performance effects of various methods.

Also Stored procedures have other advantages like Mohn mentioned in his Hacking Websites blog.

< Excerpt Begin >
Be paranoid and ALWAYS validate data coming from the client. And as far as possible use Stored Procedures. Besides getting a performance boost (since they are compiled vs SQL statements that are interpreted), they use typed parameters
< Excerpt End >


What db are you working with? I've had basic experience with Access and SQL Server.


I used to work on Access before leaning what a 'real' db is supposed to do. We worked on SQL Server here at Ncb. Access does not do most of the things I blogged about. Just has tables with Primary and Foreign keys. Probably something more!!

I guess this blog introduced Stored procedures well enough. An example later..

Dynamic Languages

Over at DevSource they have a piece on The State of the Scripting Universe. Boy, this scripting engine really is going full throtle. Everyone and his dad seems to have seen the light and gone over to scripting land. Somehow I'm still sitting in "static" darkness. We have discussed this a bit before. I guess it's the fact that I've only had very limited exposure to it... not having developed something "significant". Once you have that kind of experience under your belt it's better to compare it with C#/Java/C++.

I believe scripting in quite big in game development. A friend of mine works at a gaming company and all he does is scripting (some custom developed one) and he's in the design department! From what I understand, all games start out with the engine and you just customize that. The engine is sort of like the platform? And the scripting languages use that as an API? Maybe Dinesh can shed some light.

While on topic, Bruce Eckel had a post last month about productivity between static/dynamic languages. Productivity is one of the apparent key advantages of dynamic languages. In it he links to some dude who writes about Tests vs Type. Read his post to understand what that means.

Personally, I think the "Edit Types" block under "Explicit Typing" is way too big. To me it seems like spending time "editing types" is a way of testing. You bypass this step in "implicit typing". So I think the "editing types" part should come under tests. What dyou think?

Btw, searching for anything on the blog really sucks. I had to find the previous post link manually. Google isn't spidering/indexing the posts properly.