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Asked: 2026-06-16T00:10:59+00:00

I have a very simple java program that prints out 1 million random numbers.

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I have a very simple java program that prints out 1 million random numbers. In linux, I observed the %CPU that this program takes during its lifespan, it starts off at 98% then gradually decreases to 2%, thus causing the program to be very slow. What are some of the factors that might cause the program to gradually get less CPU time?

I’ve tried running it with nice -20 but I still see the same results.

EDIT: running the program with /usr/bin/time -v I’m seeing an unusual amount of involuntary context switches (588 voluntary vs 16478 involuntary), which suggests that the OS is letting some other higher priority process run.

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1 Answer

  1. Editorial Team

    It boils down to two things:

    • I/O is expensive, and
    • Depending on how you’re storing the numbers as you go along, that can have an adverse effect on performance as well.

    If you’re mainly doing System.out.println(randInt) in a loop a million times, then that can get expensive. I/O isn’t one of those things that comes for free, and writing to any output stream costs resources.

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