final #JVMLSThis Java video explores the relationship between final fields and immutability in Java programs. The speaker examines scenarios where final fields behave as expected, instances where they are insufficient for performance optimizations, and situations where they are excessively restrictive. The presentation uses examples and benchmarks to illustrate these points.
Immutability and Predictability: Immutable data enhances program predictability, allowing for easier multi-threaded sharing. However, Java's default mutability necessitates explicit measures (like final, records, or value keywords) for immutability.
Final Fields and Thread Safety: final fields improve thread safety by providing implicit memory barriers at the end of constructors. This guarantees that other threads will either see a null value or a fully initialized object, preventing out-of-linearity issues.
Limitations of Final Fields: final fields are not completely immutable; reflection can modify them, impacting potential JVM optimizations. This compromise was made for serialization frameworks before Java 5, although it is acknowledged as a design flaw.
JVM Optimization and Records: The JVM's optimization capabilities vary with final fields. While it optimizes access to final fields in root objects, it doesn't always perform constant folding. Records, however, often receive better performance optimizations.
Stable Values API: The Stable Value API (previewed in Java 25) offers a safer alternative for lazy initialization. It uses atomic, at-most-once mutation to achieve both lazy initialization and constant-folding benefits without the drawbacks of final fields or mutable fields with their associated concurrency issues.
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