Java Deep

Pure Java, what else

Monthly Archives: July 2014

Java private, protected, public and default

You are a Java programmer, so you know what I am talking about. public modifiers make a method or field accessible from anywhere in the application. That is the simple part. But can you tell me the difference between protected and package private? (Hint: package private is the protection of a method or a field when you do not write any access modifier in front of it. Be aware! I lie!) My interview experience is that many do not know. Do I consider that as a no go for a Java developer? Not really. You may still be a good Java developer even if you do not know that. Perhaps now you will look it up somewhere. Perhaps the Java spec is a good document to start.

I tell you something more interesting.

Literally, none of the candidates know what private is. And you, reading this article, also do not know.

Ok, this is very provocative. You may be one of the few who happen to fill his brain with such a useless information and you may even have read the Java specification.

Most Java programmers think that private methods and fields are accessible only from within the class. Some even think that only from within the object instance. They believe that

public class PrivateAccessOtherObject {
    public PrivateAccessOtherObject(int i) {
        this.i = i;
    }
    private int i;
    void copyiTo(PrivateAccessOtherObject other){
        other.i = i;
    }
}

is not possible. (It is.)

So what is private?

The recent JLS says that A private class member or constructor is accessible only within the body of the top level class (§7.6) that encloses the declaration of the member or constructor.

The example in the Java specification is not the best describing the rule. Perhaps that is just a simple example. Something like this may be better explaining the concept:

public class PrivateFieldsContainingClass {
    private static class NestedClass {
        private int i;
    }
    private NestedClass nestedClassInstance = new NestedClass();
    void set(int i) {
        nestedClassInstance.i = i;
    }
    int get() {
        return nestedClassInstance.i;
    }
}

The field i is accessible from the enclosing class as well as from inside the NestedClass. This example is also simple but more to the point that the specification example misses. Is there any real use of this possibility? Not really.

Bonus question: why did I say I was lying?

How We Chose Framework

When you develop your application most of the time you are writing code that deals with some of the resources. Code lines that open database connection, allocate memory and alikes. The lower level you code the more code is dealing with the computational environment. This is cumbersome and though may be enjoyable for some of the programmers the less such code is needed the better. The real effort delivering business value is when you write code lines that implement business function. It is obvious that you just can not make a simple decision to write only business function implementing code. The other types of code lines are also needed to execute the code and it is also true that the border between infrastructure code and business code is sometimes blurry. You just can not tell sometime whether the code you type is infrastructure or business.

What you really can do is to select a framework that fits the business problem the best. Something that is easy to configure, does not need boiler plate code and easy to learn. That way you can focus more on the business code. Well, easy to say, hard to do. How could you tell which framework will be the best on the long run when the project has so many uncertainties? You can not tell precisely. But you can try and strive for more precision. And a model does to follow does not hurt. So what is the model in this case?

During the lifetime of a project there will be a constant effort to develop the business logic. If the business logic is fixed the number of the code lines to develop that can not change much. There may be some difference because some programming language is more verbose than the other, but this is not significant. The major difference is framework supporting code. There is also an effort to learn the framework, however that may be negligible for a longer project. This effort is needed at the start of the project, say sprint 1 and 2 and after that this fixed cost diminishes compared to the total cost of development. For the model I setup I will neglect this effort not at least because I can not measure a-priori how much effort an average programmer needs to learn a specific framework.

So the final, very simplified model is to compare the amount of code delivering business value compared to the amount of code configuring and supporting the selected framework. How to measure this?

I usually… Well, not usually. Selecting a framework is not an everyday practice. What we did in our team last time to perform a selection was the following:

We pre selected five possible frameworks. We ruled out one of them in the first run as not being widely known and used. We did not want to be on the bleeding edge. Another was filtered out as closer examination showed that the framework is a total misfit for our purpose. There remained three. After that we looked up projects on GitHub that utilized one of the framework, at least two for each framework (and not more than three). We looked at 8 projects total and we counted the lines categorizing each as business versus framework code lines. And then we realized that this just can not be done during the lifetime of a human, therefore we made it simpler. We started to categorize the classes based on their names. There were business classes related to some business data and also classes named after some business functions. The rest was treated as framework supporting, configuration class.

The final outcome was to sculptured into a good old ppt presentation and we added the two slides to the other slides that qualitatively analyzed the three frameworks listing pros and the cons. The final outcome, no surprise, was coherent: the calculation showed that the framework requiring the less configuration and supporting code was the one we favored anyway.

What was the added value then?

Making the measurement we had to review projects and we learnt a lot about the frameworks. Not as much as one coding in it, but more than just staring at marketing materials. We touched real code that programmers created while facing the real problems and the real features of the frameworks. This also helps the evaluator to gain more knowledge, gives a rail to grab on and lead us where to look, what to try when piloting the framework.

It is also an extremely important result that the decision process left less doubt in us. If the outcome were just opposite then we would have been in trouble and it would have made us thinking hard: why did we favor a framework that needs more business irrelevant code. But it did not. The result was concise with common sense.

Would I recommend this calculation to be the sole source for framework selection? Definitely no. But it can be a good addition that you can perform burning two or three days of your scrum team and it also helps your team to get the tip of their fingers into new technologies.