Guilhermesilveira's Blog

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To break or not to break? Java 7?

with one comment

There is a short slide show to illustrate some thoughts. There will be better ones in the near future.

When is the right timing to break compatibility of a public api regarding its previous versions?

Well, in the open source communites there is a common sense that a library is allowed to cause some migration if there is a minor change (i.e. 1.1.5 to 1.2.0).

Whenever has a major change (i.e. 1.2.0 to 2.0.0) it might be completely rewritten in such a way that even allows its users to adopt both versions at the same time.

Some projects use the version number as a marketing technique in order to keep themselves up-to-date with their competitors.

Some products are famous for, whenever a new release appears, breaking compatibility with code written so far, requiring all programmers to rewrite part of their code. If you check Visual Basic’s life, every one-to-two years there was a major release with (usually) incompatibility.

VB programmers were used to that issue and kept coding the old projects using the previous release until the project was finished. Companies just got used to it and learned how to live on.

If your code is well tested through the use of automated tests, updating a library or a compiler/language version is an easier task because all incompatibility issues will be found prior to packing a new release of your product to your clients. testing++!

If you do not write code for your tests, as soon as you update a library/compiler/language, well….. have fun as it will probably be an unique adventure.

The java developers

Unfortunately, there is still a big part of the java community who do not write automated tests. Aside with the java legacy code that exists lacking any lines of automated tests in the world, sticking to compatibility between java releases can be seen as a good thing for the world, in general.

But for those who already write their tests, all that care with compatibility might be seen as a overestimated issue: due to the tests, we are ready to change and embrance those changes.

The java 7 crew is aware that there is a lot more that we can add to the language, but afraid because it will not preserve high levels of compatibility and usability.

What happens if the language has to worry so much about compatibility? It will evolve so slow that other languages have the chance to overcome it. This is the danger that the language itself faces. Java might not lose its position but one can find a lot more people arguing about language changes that could be done to the language – but are not… because preserving compatibility has been a main issue.

At the same time, some of the changes proposed might create huge incompatibility issues for those users who still do not write tests or that software who was not written using TDD practices. There is also another document on the same issue on the internet.

This proposes that methods defining a void return type should be considered as returning this. This way one can easily use it with Builder-patterned apis:


final JFrame jFrame = new JFrame()
.setBounds(100, 100, 100, 100)
.setVisible(true);

There are a few issues with that proposal that do not match the “let’s keep it backwards compatible” saying.

The first thing is that, nowadays, builder (or construction pattern) apis are already created returning something specific instead of void, as we can see from Hibernate‘s API, and the new date and time api.

The second point is that builders are used nowadays to create Domain Specific Languages and their implementation in Java do not use a single object because it would create a huge (and nasty) class. DSL’s are usually built in Java by using different types, i.e. the criteria API from Hibernate.

Even the given example is actually no builder api… JFrame configuration methods and real-time-usage methods are all within… itself! There is no JFrameBuilder which would build a JFrame, i.e.:


Builder b = new Builder();
b.setTitle("Title").addButtonPanel().add(cancelButton()).add(okButton());
JFrame frame = b.build();

Notice that in the simple example above, it would be a good idea to have two different types (Builder and PanelBuilder) thus the language modification do not achieve what we want our code to look like (or be used like). Instead, it will only allow us to remove the variable name from appearing 10 times in our code, making it easier for programmers to write lines of code like this:


// ugly line which has too much information at once
JFrame frame = new JFrame().setA("a").setB(2,3).setC("c").setD("d").andOn().andOn().andOn();

But why does it go against Java’s saying ‘we should not break compatibility’? Because it creates a even higher degree of coupling between my code and the api i am using.

Well, imagine that I used the swing api as mentioned above. In a future release of Swing, some of those methods might have their signature changed and therefore break my existing code. Why would an api change their method return type? Well, because if the return type was defined as void so far, no one was using it… so I can change it.

It creates the same type of coupling found while using class-inheritance in Java while using APIs. Parent methods being invoked might change their signature

Well, it was true until today. If this functionality is approved for the Java API, it will make a simple task of changing a “void” return type to something useful a hard task, where I have to think about those who have tightly-coupled their code to mine.

The questions and answers which come to my mind are…
a) is the existing Java codebase around the world usually automated tested? unfortunately, no
b) does Java want to be backward compatible? this change will not help it
c) does it want to help the creation of dsls? this change is not the solution
d) does Java want us to avoid writing the variable name multiple times? my IDE already helps me with that

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Written by guilhermesilveira

August 17, 2009 at 1:24 pm

One Response

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  1. I fully agree. Considering that returning ‘void’ returns ‘this’ feels weird. And it’s not like it’s cumbersome to return ‘this’ today.

    I’m not holding high hopes on getting fun stuff like closures and operator overloading on Java 7. I used to think that they should break backward compatibility and bring Java to this century, but then I was introduced to Scala – and now I just don’t care anymore.

    Scala is so much better in a sense that doesn’t matter how much fixing Java gets, it will never get there. They just need a decent Eclipse plugin now and then there will be great rejoice.

    Pedro Matiello

    August 17, 2009 at 10:40 pm


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