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Java · Mid-level · Theory

A colleague wrote a microbenchmark: they call a method in a loop and measure the time with System.nanoTime. The results jump around, and the first runs are noticeably slower. Why does this happen, and how do you measure it properly?

~4 min by voice

How to approach it

The interviewer wants to see whether you understand how the JVM executes code (interpreter, JIT, tiered compilation) and why that makes a naive nanoTime measurement lie. The second part is whether you know the right tool (JMH) and its techniques: warm-up, forks, statistics, protection against dead code elimination.

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jitbenchmarking
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Answer by voice

The interviewer will ask this question and listen. Think out loud and ask for a hint if you need one. When you're done, pause or tap “That's my answer”. In about a minute, your score and the points you covered show up here.

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Best with headphones · ~4 min