# Profiling & Benchmarking — Advanced Java

Source: https://www.geekswithgeeks.com/en/advanced-java/adv-profiling

> Measure real Java performance with JDK Flight Recorder and Mission Control, and write trustworthy micro-benchmarks with JMH instead of nanoTime loops.

## Tools

**JDK Flight Recorder** (`-XX:StartFlightRecording`) plus **JDK Mission Control** give low-overhead production profiling. For micro-benchmarks use **JMH** — hand-rolled `System.nanoTime()` loops are wrecked by JIT warm-up, dead-code elimination, and loop hoisting.

## A JMH benchmark

JMH warms up the JIT, runs many iterations, and forks a fresh JVM per benchmark so results aren't skewed by earlier runs in the same process.

```java
@Benchmark
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public int sumLoop() {
    int total = 0;
    for (int x : data) total += x;
    return total;
}
```