Utkarsh Sengar

Software, Growth @upwork, ex-@OpenTable, @ebay, @RedLaserApp, build side projects at thearea42.com, life long learner, always up to something, 🚀

xkcd: Random Number

I have always used Random’s nextInt() or nextLong(). So was curious on how “random” is it actually? Then I found this protected method next().

protected int next(int bits)

Implementation of Random.java via Google code: protected int next(int bits) { long oldseed, nextseed; AtomicLong seed = this.seed; do { oldseed = seed.get(); nextseed = (oldseed * multiplier + addend) & mask; } while (!seed.compareAndSet(oldseed, nextseed)); return (int)(nextseed >>> (48 - bits)); }> The general contract of next is that it returns an int value and if the argument bits is between 1 and 32 (inclusive), then that many low-order bits of the returned value will be (approximately) independently chosen bit values, each of which is (approximately) equally likely to be 0 or 1. The method next is implemented by class Random by atomically updating the seed to> (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1)> and returning> (int)(seed >>> (48 - bits))> This is a linear congruential pseudorandom number generator, as defined by D. H. Lehmer and described by Donald E. Knuth in The Art of Computer Programming, Volume 3: Seminumerical Algorithms, section 3.2.1.


EDIT: Something even more interesting: Why this code is giving strange result? So Random?

Link to JavaDocs for Random.