Category: java

Design patterns were not born equal. Some of them are boring, while others are special. Do you remember your feelings after learning what the Data Transfer Object is? Don’t remember? Of course – cause you didn’t have any special feelings about it other than “It’s easy”.

What do you say about Singleton? Yeah, this is kinda interesting pattern which gave you something to talk about. Do we really need it? Can’t we just achieve the same effect with static variables? Does it make your entire application tightly coupled? Lots to discuss and share your opinion in online forums.

How about Visitor? You must have remembered those feelings when you ran into it first time. The day when you understood how the Visitor pattern works was crucial in your career – that was the moment when you realized that you were not junior software developer anymore. From that very moment you can consider yourself a mid-level person. Till when? Till you’ll be able to explain the Visitor pattern to at least three juniors. Continuos Explanation (c) might reveal though that Visitor is not exactly what you originally thought it was, but now you really get it!

But there is one pattern that has a very strange effect on people. It’s called Dependency Injection. Decoupling in action! A Customer class doesn’t need to reach out for its Orders! How cool is that! First, it gets you high just like smoking banana peels. Then it makes you a little depressed when you realize that there is always a price to pay – instead of having two simple classes Customer and Order you need to have an Inversion of Control container and should neverforget to properly annotate the injector and injectee. In the server-side Java, containers are not too bad, really. We are used to them and feel pretty comfy inside.

But then, a senior Java developer starts learning other domain-specific programming languages like ActionScript or JavaScript just to realize that these poor people don’t have any IoC containers yet! Can you believe that? This is when the Java developer gets craving to make the lives of those (not as fortunate) ActionScript or JavaScript developers easier. In other words, such DI addict wants to share the needle with the rest of the world and inject, inject, inject… This results in proliferation of the “lightweight” DI frameworks/IoC containers among UI developers, which they should be using on top of whatever framework you currently use. This will overcomplicate the application design, but will allow you to inject Orders into Customers rather than using this so-nineties-getOrders().

Oh well, why did I poured all this on you? I don’t know. But please don’t try to tell this to people who enjoy living in thes IoC worlds or else they’ll become aggressive again and will make you feel stupid for not realizing that one can’t do a proper unit testing without the DI. Do we need unit testing? OK, OK….I won’t even go there.

Currently I’m teaching a Java class online, and Vitaly O., one of my students, ran into an interesting situation. He sent me the program below, which, to his surprise, printed 1.

public class Main {

    public static void main(String[] args) {
        Integer t = new Integer(0);
        t=1;
        test(t);
        System.out.println(t);
    }
   
    public static void test(Integer t) {
    	t=2;
    }

}

The topic of passing by value vs by reference is one of the difficult topics to understand for Java beginners. The code above can confuse junior Java developers, because the author of the program above ran into a bouquet of Java features, which I’ll explain (slowly) in this blog.

All Java textbooks (mine included) will tell you that objects are being passed by reference and primitives by value. That’s fine and understandable – nobody wants to copy large objects in memory . But what about the variables that point at an object and are being passed to a method as arguments like in test(t) line above?
First, let’s take care of a simpler case. Let’s replace the Integer with the class Car that looks like this:

public class Car {
   int salesmanWhoHasKeys;
} 

Imagine a tiny car dealership with two salesmen that has a room only for one car. When a customer pops in, one of the salesmen takes the car keys to test drive THE car. The class TestCar will look similar to the class Main, but is not exactly the same.

public class TestCar {

    public static void main(String[] args) {
        Car t = new Car();
        t.salesmanWhoHasKeys=1;
        
        test(t);
        System.out.println(t.salesmanWhoHasKeys);
    }
   
    public static void test(Car t) {
    	t.salesmanWhoHasKeys=2;
    }
}

The program TestCar prints 2. Why? What makes it different from the program Main? Just bear with me for a moment. Let’s completely understand what the phrase “objects are passed by reference” means. There is only one car, remember? And Java doesn’t create a copy of the one and only instance of the object Car just to pass it to the method test(). But it does create a copy of the original pointer t inside the method test for method argument, which (to add to the confusion) is also named t.

Get used to the fact that we have one object in memory with two different pointers to it (t and ttt). To make things easier to understand, modify the method test() to look as follow:

   public static void test(Car ttt) {
    	ttt.salesmanWhoHasKeys=2;
    }

The program still prints 2. So what’s the difference between dealing with the instance of a Car vs Integer? The wrapper class Integer is immutable. This means that you can’t change its value once it was assigned, which is not the case with the Car.
To make things worse for comprehension, the Java feature called autoboxing kicks in and the original program quietly creates instances of new wrapper Integer objects when it sees something like t=2. This line gets converted into t=new Integer(2)! Got it? So the value 2 has been assigned to a different Integer object via a different variable t.

And just to make sure that you clearly understand the whole confusion of the program Main, please answer my final question, “How many instances of the class Integer were created during the lifespan of the program Main?”

Who said two? Mary? Wrong! The right answer is three! The first one had the value of zero, the next line caused the creation of the another instance if Integer with the value of 1, and the third instance was created by the method test() with the value of 2. Don’t believe me? Step through the Main program in a debugger, and you’ll see three different ids assigned to the variable t.

Don’t you love Java? I do.

Presently I work for a client that has an open floor setup, which means that lots of noises and conversations are happening at any given moment. But I prefer listening to the music while developing software, and  the Internet radio Pandora really helps. I’ve created several radio stations, and based on my mood, I listen to a hard rock, jazz, blues or other genre.

Since there is no free lunch, Pandora used to insert audio commercials between the songs. No problems here. I understand. This morning, I noticed that Pandora got a facelift, and it seems that the main reason was to free some screen real estate for visual advertisement. Now it’s getting annoying.

All of a sudden, my browser’s window became fool  of women. This is no good. I’m working here, guys.There are people around me. They pay me well for developing software. And what do they see? Are we paying Yakov for having fun staring at all these women?

But things got even more interesting.  I noticed that all these beautiful ladies were black. This got me thinking why would Pandora assume that I’m specifically interesting in black women? The title on the top of the screen read something like “Find local black women in your area.” This is when having analytical thinking helps. At the time, I was listening to the radio station that  was playing reggae music. Got it?

After a while, I switched to another radio station that was playing Joane Osborne and the likes. Guess what? The browser’s window got filled with the faces of white women.

I suspect that Pandora is trying to be smart in showing context-sensitive ads targeting the proper audience.Do they assume that people listening to reggae are most likely into black women and fans of Joanne Osborne are whites?

So far it’s just my assumption, and would require a lot more hours spent listening to various types of music. I like women. I really do. There are gorgeous white, black and latino women (the rumor has it that J. Lo is available again). My question is, what kind of radio station should I create to see all of them at once and not in a into-your-face manner? If I won’t find the answer, I’m going to have to shell out 36 bucks for a year of ad-free Pandora.

Oops…It’s getting even more interesting…Here comes a large banner offering me “High Quality Generic Viagra”. Guys, I may lose this contract with my client, and won’t have money to buy high quality blue pills from your sponsors.

I always get excited when I see another person questioning the use of frameworks that ask you to either replace one language with another or write additional code as a life support to sustain the framework’s functioning. This time my kudos to Christin Gorman, who did a great job explaining why using the Hibernate framework over SQL is a bad choice.  Watch this video , where Christin uses the Cake Mix metaphor to deliver her message loud and clear.

In the past I was using a different metaphors. One was about the goat and rabbi. The other one is about the Axe Soup a.k.a. Stone Soup.  I remember this story about a soldier returning back from war. He was very hungry, and, when reached some village, he asked a women living there to give him some food. She rejected. Then he asked for a pot of water so he could cook a soup form his axe. She became curious and agreed. After placing the axe in a boiling water he asked if she had just one small potato to add some flavor to the Axe Soup. She gave the potato. Than he asked the woman about a small onion, and on and on and on.  When the soup was ready, he removed the axe from the pot and fed himself with a tasteful soup.

This is pretty much the situation in many enterprise IT shops that blindly prefer using frameworks to the programming language itself.  If you didn’t get the analogy, Hibernate ORM framework is an axe. Add it to the project (the pot), then write some HQL queries, which is a replacement of SQL, learn and use a couple of dozen annotations, and after all this is done you won’t need to worry about JDBC.

Well, you may need to fine tune the HQL,  but it’s later…But now we are covered. We are hibernating as everyone else, yay!  If something will ever go wrong, we can always remove Hibernate from our code, right? Sure, the same way as the soldier pooled out the axe from the soup, when his project was complete.

I really like many improvements that made Java EE 6 light , easy, and really helpful. I like the concept of pruning, which means gradually getting rid of the useless JSRs. But if you ask me, I’d pruned JPA 2.0 without thinking twice. The goal of this 500-page spec is to replace SQL with another language. Why? I don’t know.

Cristin is right, professional chefs never use cake mixes. But, unfortunately, the modern IT shops are more like the fast food chains than Michelin restaurants.