sun.misc.Unsafe memory access deprecated

Java 23 Course · lesson 9 of 15 · 4 min read

The long goodbye to the API half the ecosystem secretly depends on.

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Key points

  • sun.misc.Unsafe was never public API, but Netty, Cassandra and countless libraries use it.
  • JEP 471 deprecates its memory-access methods for removal, starting a multi-release wind-down.
  • The supported replacements already exist: VarHandle for fields, the FFM API for off-heap memory.
  • You will usually hit this through a dependency, not your own code, so upgrade libraries early.
  • Warnings appear first, then the methods throw, then they disappear - do not wait for the last step.

You will meet the Unsafe removal through your dependencies, so track their JDK support, not just your own code.

ZGC generational mode by default Class-File API (2nd preview)

This is a reading copy. The full lesson — with the visual explainer, the interactive lab and a Run button for the code — lives in the Java 23 Course course, and every lesson in it is listed on the Java 23 Course contents page.