Create an Array with random numbers

Question

How I do create an array of size 256 with sorted random numbers in the main method? I want to create an array that randomly generates numbers between 1-256, the size would be 256 as well which means it would have 256 numbers in the array and they're sorted. My code only returns me zero?

public class Array {
    public static void main(String args[]) 
    { 
        double[] randomarray = new double[256];
        for(int i = 0; i<randomarray.length;i++)
            randomarray[i] =  Math.random();
        
        for (int i = 0; i<randomarray.length;i++)
            System.out.println(randomarray[i]);
    }
}

Try int[] randomarray = new Random().ints(256, 1, 256 + 1).toArray(); — user4910279
– user4910279, Commented Jun 30, 2020 at 23:38
I don't know how you get zeros. Math.random() gives you pseudo-random numbers from 0 to 1 so you can just multiply it by your range e.g. 256. — F. Müller
– F. Müller, Commented Jul 1, 2020 at 0:22

Basil Bourque · Accepted Answer · 2020-07-01 01:12:01Z

4

Streams

As @saka1029 commented, the easiest (less code) way is by creating a IntStream, a stream of int values, produced by a call to Random.ints.

int[] sortedRandoms = 
    new Random()              // Access a random-number generator.
    .ints(256, 1, 256 + 1)    // Generate a stream of int values, an `IntStream` object.
    .sorted()                 // Sort those generated `int` values.
    .toArray();               // Return the generated `int` values in an array.

here I added sorting as well.

edited Jul 1, 2020 at 1:12

Basil Bourque

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answered Jul 1, 2020 at 0:00

karakfa

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1 Comment

Basil Bourque Over a year ago

Good Answer. As a habit, I would use ThreadLocalRandom rather than Random.

Putnam · Accepted Answer · 2020-06-30 23:34:03Z

2

Math.random() returns a double between 0.0 and 1.0, and casting to an int floors doubles, so you're setting all of your array members to 0. You'll need to multiply Math.random() by your desired max value before you cast it to int.

answered Jun 30, 2020 at 23:34

Putnam

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1 Comment

President James K. Polk Over a year ago

@Jack: Read the last sentence of the answer. Don't post significant code in comments please.

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