Generating a sequence of Pseudo-random numbers based on a seed

Question

In Java, I want to generate a program that generates a string of around 15 numbers based on a seed. It always needs to be from 1 to 9. It should seem random, but each seed spits out the same sequence. For example if you type the number 5, it might output 194639573978476, but if you enter 6, it would output 657362047273958, and 5 will always output 194639573978476. How do i do this?

Hi, have a look at this post : http://stackoverflow.com/questions/12458383/java-random-numbers-using-a-seed — Sylvain GIROD, Jan 08 '17 at 00:30
I have seen that, but I still can't see how to do what I want — MrSam123, Jan 08 '17 at 01:30
Just google for "using random with seed in java" and "generate random string in java". It isn't hard. — Tom, Jan 08 '17 at 02:40

score 1 · Answer 1 · answered Jan 08 '17 at 03:06

First :If two instances of Random are created with the same seed, and the same sequence of method calls is made for each, they will generate and return identical sequences of numbers.

Source:Oracle

For this reason the seed needs to be different every time to generate a different numbers. You can use the time as seed. Like this,

Random random = new Random(System.currentTimeMillis());
StringBuffer sb = new StringBuffer();

for (int i = 0; i < 15; i++) {
    sb.append(Integer.toString((random.nextInt(9) + 1)));
}

System.out.println(sb.toString());

Sample output every time you run the code:

146645139262732
919846574753947
662686147977574

Hope this helps!

score 0 · Answer 2 · answered Jan 08 '17 at 01:52

First, create an instance of Random and give it your seed as an argument:

Random rand = new Random(seed);

Then just get 15 numbers. You can use a stringbuilder to build the string, or any other way you want. Shouldn't be too hard, but here's a quick and dirty way to do it:

String result = "";
for(int i = 0; i < 15; i++) {
   result += rand.nextInt() % 9 + 1;
}

Please note this is some very dirty programming, did it this way for the sake of simplicity and readability. This is very poor style and you shouldn't copy paste this without changing it.

Generating a sequence of Pseudo-random numbers based on a seed

2 Answers2