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J2SE and Open Source - Living Together in Perfect Harmony

Preserves the integrity of the language

Open source and J2SE,
living together in perfect harmony
Side by side on my computer keyboard,
Oh yeah, why can't we?

Java has been the springboard for some of the most successful open source projects today including JBoss, NetBeans, and Eclipse. Several folks though have felt the missing piece was an actual open source implementation of the runtime. Some view Sun's stewardship of Java and the JCP as being too controlling, while others believe it is an essential benign rule that preserves the integrity of the language. The view taken by Sun execs is that the JCP is essential to preserve portability while preventing forks in the language (as Microsoft once attempted with proprietary extensions). Should these occur, they could compromise a user's expectation that a Java program, once written, can run anywhere. Advocates of open source, however, deny this would occur and cite successful projects in which the benefits of fast innovation and widespread adoption have been fueled by having an open source community of developers who drive the implementation forward.

Earlier this year the Apache Foundation announced the Harmony project. Its aims are to write an open source version of J2SE from scratch. Given that specifications for J2SE are freely available, one question might be why such a move hasn't occurred before? In the FAQ for Harmony, Gier Magnusson from Apache states: "While the Java Community Process has allowed open source implementations of JSRs for a few years now, Java 5 is the first of the J2SE specs that we are able to do due to licensing reasons" (http://mail-archives.apache.org/mod_mbox/incubator-general/ 200505.mbox/%[email protected]%3E).

Rather than reinvent the wheel, after the initial announcement it seems that the plan is to try to pollinate the project with code and ideas from existing Java runtimes. At JavaOne Geir said: "There is a lot of software out there that we are hoping can be donated. We are hoping that we will get seeded with some code from existing production Virtual Machines." This is an invitation to the big guns of software and mom and pop developers, many of whom have either privately or openly tinkered with creating their own implementations of Java.

There are several potential Harmony contributors who might be in Geir's sights to step up to the plate. BEA has a very good JVM implementation in JRockit (www.bea.com/framework.jsp?CNT=index.htm&FP=/content/products/jrockit), while Kaffe (www.kaffe.org/) is a clean room implementation of the JVM.

Making Harmony succeed, however, requires more than just a JVM, as J2SE contains many lines of code in the actual class libraries, all of which need API compatible reimplementation. Due to licensing and IP issues this most likely must be done in an environment without reference to the existing Sun J2SE source code base, so the hill to climb is steep and high one.

I usually don't pay much attention to the cries of doom issued by execs of any company that has a vested interest in whether open source Java should succeed or fail, but I was surprised to hear James Gosling, when asked about Harmony, raise the issue of why Apache wants the Harmony license to be different from the existing J2SE one. He said: "I understand why they would like it to be different. From our point of view that would actually be more destructive than helpful. It boils down to forking: they believe that the ability to fork is an absolutely critical right" (www2.vnunet.com/lite/News/1163182). His voice is one I respect and should be listened to as words of wisdom and caution so the worst case scenario doesn't become a reality. To ensure compatibility with J2SE, however, the harmony FAQ states that it will be verified against the J2SE Test Compatibility Kit. The TCK is published by the JCP and is the yardstick used by all ratified J2SE integrations (JCP or commercial) that to date has ensured no fragmentation exists and no compromise of integrity has occurred.

Whatever the outcome of the Harmony project, while I do understand the concerns of those who are frightened of fragmentation in the language, I am more excited by the prospects of having an open source implementation J2SE. This will enjoy the same benefits that other open source projects have experienced, where a community of like-minded, smart individuals who share the same goal can participate equally in the same code and knowledge base of ideas and innovation. Ideas, bug reports, and schedules are transparent and can be iterated in public toward the best solution. The momentum of the project becomes fueled by the feedback loop created by an alliance of like-minded individuals in a partnership of conviction. To those who don't believe this will work, ask not if the glass is half empty, but listen instead to the lyrical genius of Sir Paul McCartney and Stevie Wonder:

We all know that people are the same where ever you go
There is good and bad in everyone
Learn to live, we learn to give each other
What we need to survive, together alive

More Stories By Joe Winchester

Joe Winchester, Editor-in-Chief of Java Developer's Journal, was formerly JDJ's longtime Desktop Technologies Editor and is a software developer working on development tools for IBM in Hursley, UK.

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Most Recent Comments
JoeWinchester 08/16/05 11:46:40 AM EDT

Hi Alex,
But there are already different versions of the JRE created by different vendors for their particular hardware platforms. Sun does not create the Z-OS or iSeries JRE. What keeps these together is the TCK and given that Java works now cross platform, all that is different is that there can be an open-source version of J2SE. James' comments were more about the fact that open-source J2SE would create forking and this is something that I agree with we don't want. What I don't understand fully is why forking is more likely with open-source that occured before with different JRE's being created commercially.

Alex 08/12/05 02:45:35 AM EDT

I agree with James Gosling's concern - there will always be holes in any specifications.

If there is only one single implementation, such undocumented behaviours can still be utilised after some preliminary investigations; but if more than one implementations is used by the majority of end-users, these undocumented portions could have different behaviour.

It may sound as if we shouldn't have used any unspecified "features" in a specification, but they are often the only workaround for certain tasks to date, due to the deficiency in the spec. Only by having a single major implementation can we do away with these problems easier, if at all.