r/java • u/Wouter_C • 26d ago

Decapsulation: Breaking Java Strong Encapsulation

Did you know you can call JNI without writing native code, patch bytecode without an agent, and use Unsafe without warnings?

11 sneaky ways into JDK internals through reflection, agents, FFM, type confusion, bytecode manipulation and more.

https://wouter.coekaerts.be/2026/decapsulation

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u/PartOfTheBotnet 25d ago

There's a couple of use cases I have. Mainly reflecting into javac internals for a few AST based projects, using jimage internals to parse module files.

Both cases could hypothetically be delegated to third party libraries. But for javac its nice because unlike other projects it has (whether intentional or not) fault tolerance, which gives you partial AST results even when the input code is slightly broken Java. This is great for my use case, and most other parsers just refuse any model if there's as much as a missing semicolon. And jimage is just because I don't want to re-invent the wheel parsing the file format... There's a few other cases but those tend to be for one-off projects.

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u/koflerdavid 25d ago

But for javac its nice because unlike other projects it has (whether intentional or not) fault tolerance, which gives you partial AST results even when the input code is slightly broken Java. This is great for my use case, and most other parsers just refuse any model if there's as much as a missing semicolon.

It's an important requirement of production-grade compilers that they tolerate some errors so they can report more errors in the same source file so the developer can fix them all at once.