Interpreter, JIT, and Hot Code
The JVM can interpret bytecode and compile frequently executed code to native machine instructions using JIT compilation. Runtime profiling allows optimizations such as inlining, dead-code elimination, escape analysis, and speculative optimization.
Bytecode
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+--> Interpreter --> execution
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+--> JIT compiler --> native code --> optimized hot path
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+--> deoptimization if assumptions fail
This means startup and steady-state performance can differ. Benchmarking Java requires warm-up, realistic workloads, and proper measurement.
Benchmarking
Do not conclude that one Java implementation is faster from a tiny cold-start benchmark; JIT warm-up matters.
Key Takeaways
- JIT compilation is profile-guided and runtime-aware.
- Optimized code can be deoptimized when assumptions fail.
- Use proper benchmarking methodology.