Sven Woltmann • 4/7/2025

Java Compact Object Headers (JEP 519)

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This technical article details Java's Compact Object Headers introduced in JEP 519 (Java 25). It explains how the feature compresses the standard object header from 96 bits to 64 bits, reducing heap memory usage. The article covers the structure of object headers (Mark Word, Class Word), the transition from legacy mechanisms, and the performance benefits of this memory optimization within Project Lilliput.

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#jvm #memory optimization #Java
Java Compact Object Headers (JEP 519)

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