Adam Bien says Jigsaw should increase the classloading performance and reduce the size of jars. It will come with JDK 1.7 and is now part of the openjdk project. He says it makes the incremental modularization of legacy projects easier.
In the article you say
"It will be shipped with every Oracle / Sun JDK 1.7"
What about other vendors' JDKs? Will it be optional for them to ship an implementation, and if so what would that mean for interoperability?
I think the implementation of the classloaders has no effect on the compatibility between different JDKs. The fundamental thing is that the JVM'spec API is the same for all implementors.
Class loading performance is a strange thing to focus on for jigsaw.
The main benefit is finally cleaning up the encapsulation of modules in everyone's code. That's a huge benefit for anyone who wants to properly modularize the visibility of classes and methods.
Compared with the benefits to be gained from code clarity, the classloading effects aren't barely worth mentioning.
Can anyone tell me the main advantage(s) of Jigsaaw over separate jar + maven pom?
The main benefit, for me, is the module visibility in your class definitions. The jar changes aren't much different from Maven, except that it's integrated in the language instead of a separate XML file.
With the changes, you can define "module void foo()", or "module class MyClass", which has visibility only within the module, but isn't accessible outside of the module. From a code-self-documenting perspective, it will be nice to give a clearer description of your programming intentions. And code readability is key.