Nov 05 2012

Learning Spring, part IV

Category: TechnicalIuliana @ 13:05

<ref local=””/> vs. <ref bean=””/>

So, when should we use one or the other and why?

First, I’ll offer you a link to the official Spring reference documentation related to this subject.  Basically:

Specifying the target bean through the bean attribute of the tag is the most general form, and allows creation of a reference to any bean in the same container or parent container, regardless of whether it is in the same XML file. The value of the bean attribute may be the same as the id attribute of the target bean, or as one of the values in the name attribute of the target bean.

And:

Specifying the target bean through the local attribute leverages the ability of the XML parser to validate XML id references within the same file. The value of the local attribute must be the same as the id attribute of the target bean. The XML parser issues an error if no matching element is found in the same file. As such, using the local variant is the best choice (in order to know about errors as early as possible) if the target bean is in the same XML file.

Then we will play with some source code.
Continue reading “Learning Spring, part IV”

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Oct 13 2012

Learning Spring, part III

Category: TechnicalIuliana @ 18:15

I have a new hot question for you:

We have two classes AccountServiceImpl and ClientServiceImpl. Any of these classes inherits from each other, meaning one is a subclass of the other. What will happen if we define a pointcut like this:

"execution( * *..AccountServiceImpl.update(..)) 
       && execution( * *..ClientServiceImpl.update(..)) "

And here are your options:

  1. The pointcut matches any public update methods of the two classes whatever the arguments.
  2. The pointcut matches any update methods of the 2 classes whatever the arguments and the method visibility.
  3. The pointcut matches any update methods of the two classes, with one ore more arguments and whatever the method visibility.
  4. No join point is defined.
  5. Something else will happen.

Continue reading “Learning Spring, part III”

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Oct 10 2012

Learning Spring, part II

Category: TechnicalIuliana @ 17:02

One of the reasons I haven’t taken SCJP yet was the stupidity of the grammar in the construction of some questions and answers on the exam.(I have given examples in the past on this blog, search a little if you are curious)  Currently I am to take the Spring Core Certification exam and  and I am terrified that I will find the same kind of questions and answers in it.  And the worst part is that there are not that many mock exam samples on the internet, so I have no chance to get used to the specific style.

For example:

In Spring Framework’s declarative transaction implementation , is it sufficient to annotate the classes with the @Transactional annotation ?
Select Your Answer :

  1. No
  2. Yes
  3. No . <tx:annotation -driven/> has to be added in configuration file

You might be inclined to say that the correct answer is 3, Continue reading “Learning Spring, part II”

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Sep 15 2012

Learning Spring

Category: TechnicalIuliana @ 23:47

A few months ago the company where I am currently employed sent me to Belgrad to train me in Spring Core. The training lasted 4 days and at the end I was supposed to take the Spring Core certification exam and pass it.

I delayed that for a while, but because now I have some spare time I decided it was time for me to do this thing. So I went over the slides and the spring code samples again. But after doing some mock tests I concluded I will most likely fail the certification, because the official materials were not enough so I started reading Spring in Action. Still I noticed that in the tests there was still stuff that I hadn’t covered. So I started reading Spring Reference. And because I have some problems in retaining information just by reading it, I stared to test the recommended examples. And this is where I hit some walls.

But before telling you what is not clear for me I shall tell you what technologies I’m using for development: Maven 3.0.0, Jdk 1.7, Intellij Idea 11.1.3 and Spring 3.1.2 (I know the certification is for 3.0, but as the Spring reference manual has 840 pages, I might as well read about the new and useful stuff added in 3.1)

The first problem I had was with the compound property names. I tried using them. Idea does not recognize them and my test fails.

Continue reading “Learning Spring”

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Jul 17 2012

Brain overload

Category: TechnicalIuliana @ 12:32

If you are a developer and write error messages like these :

– Simple Error bla bla bla
– Small Malfunction bla bla bla

And I end up working with your code I have only this to say:

I don’t know who you are, I don’t know what you want, If you’re trying to be funny, I can tell you I don’t have a sense of humour, but what I do have are a very particular set of skills, skills that have acquired over a very long career. Skills that make me a nightmare for people like you. If you stop writing shit debug messages like these now, that will be the end of it. But if you don’t, I will look for you. I will find you and I will kill you.

Because when it comes to code, there is no such thing as a Simple ERROR, nor a Small MALFUNCTION.


Jun 19 2012

when you have an itch…

Category: TechnicalIuliana @ 10:34

… you gotta scratch it. And I had a serious itch caused by my Windows. Even if Windows has evolved so much, even if Windows 7 is the peak of greatness among all the Windowses before it, it still does not know how to manage 4 core processors. So I was seriously pissed about the fact that Windows 7 froze from time to time, making my super-laptop look like my first computer, an AMD K6, 500 MHz and 256 MB SRAM. Which was definitely not cool, considering the fact that my laptop’s configuration looks like this: Intel Quad Core i5-450M and 6 GB DDR3. The only reason I kept windows so far on my laptop was that my processor has a capability known as turbo boost, meaning that can over-clock itself when needed. But this won’t be needed that much if the tasks were efficiently distributed between the 4 cores, which were not.

So two days ago, I just snapped, decided to give up the possibility of playing games for a while and went on a search for the perfect Linux for my laptop. I am fond of Gentoo as you know, but compiling a full OS was not an option because it is a time-consuming operation and also because all that compiling would set my laptop on fire and it’s already hot in Romania right now (32 Celsius degrees). So I was left to choose between Archlinux and Mint. I did not even consider Ubuntu, it’s a Linux that looks and acts like Windows, the thing I was trying to get rid of. I had Archlinux before and I know in order to get the final result some time must be wasted on its configuration, so I went for Mint.

In less than 30 minutes I had a fully functional and compact Linux, oh well … fully for a normal user, not for me, a curios developer. So after this I went on and started installing the development software. The first one I wanted to install was the JDK. Mint uses open-jdk which Idea and STS refuse to go along with, so I went on a quest for installing the Oracle version. If on other Linux systems this was a piece of cake on Mint, it was not so, because Mint has all these symlinks pointing to open-jdk binaries, and even if you do everything right, set the JAVA_Home variable and add it to the path, when you will execute “java -version” in the console, the binary that will be executed will still be the one of the in the open-jdk. The only way to change this is to go to /usr/bin, see where the specific symlinks point to and change that. After that I installed Idea and STS and everything was flawless.

Then I wanted to add a second monitor and this is where all blew up in my face. But not because there was something wrong with Mint, but because one of the cables was not plugged in correctly in my monitor and the system did not see it. I did not even consider that the problem might come from a cable and went on and tried to install nVidia drivers in order to convince the system to see my external monitor. After the first restart I was left without an interface, because the nVidia drivers were not stable, of course. So I went old-school and installed lynx, a text based browser, and searched for a solution for my problem. I did so and tried different options for an hour, when finally it worked and I had my graphic interface back, but the external monitor still was invisible to Mint, so I considered the possibility of the monitor not actually being plugged in the laptop. I check the cables and … surprise. It detected it right away.

Conclusion: if you want to install a Linux on your laptop, I truly recommend Mint, it is small, smart, fast and it knows how to work the special buttons on your laptop, without any additional settings. And is also easy to install, if you are not an old-school developer who considers problems being caused by the software first :D , that is. :)

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May 05 2012

What does a passionate developer do…

Category: TechnicalIuliana @ 22:35

… when is stuck in a hotel room because of the rain, bored out of his mind and with no mood to work? Well when that happens to me I start to reed my java feed reader and depending on what I find there I might write my own articles. So… yes, this article is today’s consequence of boredom.

1. What is the flaw with the Stack class?
Actually, there are two of them all being caused by the fact that java.util.Stack extends java.util.Vector:
I. Extending Vector methods insertElementAt and removeElementAt can be called and they actually work, so the stack definition is not respected (that part with only the last inserted element being accessible, the LIFO principle)
II. Extending Vector, Stack is also synchronized which makes it slow and when synchronization is not necessary this  is quite inefficient. This is not exactly a flaw, it’s more of a personal observation observation.

Then again in the api it is written that “It extends class Vector with five operations that allow a vector to be treated as a stack “, so I guess these are not flaws, the Stack class just works as intended. (Recommendation: use ArrayDeque)

2. Can an interface extend multiple interfaces?
There is no right answer to this question, because it depends of the point of view of the interviewer.
I. Yes, because you can define an interface like this:
public interface MultipleIntf extends List, Serializable {
}
II. No, extending means actually inheriting all functionality of the super-entity and  perhaps adding new functionality, in the case of interfaces there is nothing to inherit and no functionality to add. Except for the obligation to implement all abstract methods that will be enforced on the implementing class.

3. What is lazy loading?
Lazy loading is a name to describe the process of not loading something (object/class) until needing it. This question will surely take you to a ClassLoader discussion, so it is better to know and understand the Java Class Loading mechanism.
So:
– the java source files are compiled into executable code for the JVM, called bytecode, stored into *.class files.
– at start-up JVM has no loaded classes. When the first class is loaded, the classes on which its execution depends are searched and loaded too. So if I have a class which has imports statement for ArrayList and Serializable, the JVM will load my class, then it will search and load ArrayList.class and Serializable.class. Let’s imagine we have a big application with a lot of class files and one of them is missing. The application will run just fine, until we try to access a functionality implemented by that class, when the JVM will let us know that the class was not found by throwing a java.lang.ClassNotFoundException.
And this my darlings is lazy loading. A class is not loaded until used and there would be no point in doing that for efficiency reasons. Right? Anyway, if you want to have a deep understanding of the Java Class Loader, I recommend this article.

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