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In Java we have static class Math. You don't need to create its objects so its static. Another one is Random class. We don't need to create its instances so why isn't it static too? My classes I often use random numbes and get mad when have to create field rand in every class to generate random numbers. So why isn't it static?
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Note that just like all other methods of the Math class, Math. random() is a static method so you can call it directly on the Math class without needing an object. It returns a value of type double .
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These created values are not truly "random" because a mathematical formula is used to generate the values. The "random" numbers generated by the mathematical algorithm are given a starting number (called the "seed") and always generates the same sequence of numbers.
Random number generators are really only pseudo-random. That is, they use deterministic means to generate sequences that appear random given certain statistical criteria. The Random(long seed) constuctor allows you to pass in a seed that determines the sequence of pseudo-random numbers.
The Random class has state, including where it is in its sequence, as the values produced are not truly random, just a pseudo-random sequence.
This can be demonstrated by initialising two instances with the same seed.
Random a = new Random(123); Random b = new Random(123); for (int i = 0; i < 5; i++) { System.out.println(a.nextInt() + "," + b.nextInt()); } Output
-1188957731,-1188957731 1018954901,1018954901 -39088943,-39088943 1295249578,1295249578 1087885590,1087885590 If you create with the default constructor Random(), then the seed is initialized based on the current time in nanoseconds + a static counter, which means different instances are very likely to have different sequences.
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