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While using a general data transport format instead of Java object serialization is great for most applications it cannot replace all usecases.

JVM based distributed grid computing services use Java object serialization to distribute queries throughout the grid. This allows users to write their queries as arbitrary Java code which will be executed on every node without having to deploy the code on every node.

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How does that work? You describe a situation in which code that does not exist on a given node is executed on that node nonetheless.

You write a query that is wrapped inside a serializable object. The object with your code inside is serialized using Java object serialization and distributed to every node. Each node is now able to execute your query based on Java code.

https://ignite.apache.org/features/computegrid.html

This isn't a native feature of Java serialization. Class implementations are not included in the serialized data.

> How do closures get shipped around?

> Every closure is an object of a particular class. When the closure is being sent it gets serialised to a binary form, send over the wire to a remote node and deserialised there. The remote node should have the closure's class in its classpath or enable peerClassLoading in order to load the class from the sender side.

https://apacheignite.readme.io/docs/faq

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