CODEWITHSUNDEEP
javarandom
user2970322
user2970322

Reputation: 1

How can I fix the size of randomly 5 generated numbers?

I am randomly generating numbers using java.util.Random. But, I can not keep the length of the numbers fixed. Can you help me please?

Upvotes: 0

Views: 137

Answers (4)

nheid
nheid

Reputation: 1108

If you're ok using libraries:

RandomStringUtils.random(15, "12345")

would give you Strings like: 124444211351355 of length 15

I just happened to write a post about that (shameless self-advertising link: http://united-coders.com/nico-heid/generating-random-numbers-strings-java/)

Upvotes: 0

user289086
user289086

Reputation:

The first thing to consider is that an int cannot hold 15 digits. It just can't. It can only go up to 232 -1, which is 9 digits long. A long can hold up to 19 digits - but if one wants to solve for the general case, it is necessary to use the BigInteger package instead.

Remember that BigInteger is an immutable object (like String) and thus you must assign the value back when looping.

package com.michaelt.so.random15;

import java.math.BigInteger;
import java.util.Random;

public class Main {

    public static void main(String[] args) {
        Random r = new Random();
        BigInteger result = BigInteger.ZERO;
        for(int i = 0; i < 15; i++) {
            result = result.multiply(BigInteger.TEN)
                           .add(BigInteger.valueOf(r.nextInt(5)+1));
        }
        System.out.println(result.toString());
    }
}

It starts out with the value ZERO, and loops through for 15 times, each time first multiplying the value by 10 (another BigInteger preallocated value) and then adds the new value into the 1's position. It does this 15 times.

When done, one can get its value as a string or long or other format - or continue to use it as a BigDecimal (necessary if you should ever decide you want a 20 digit long value).

Runs of the above code produce output such as:

313455131111333
245114532433152
531153533113523

Upvotes: 0

blacktide
blacktide

Reputation: 12126

To fix the length of a randomly generated number, generally you'll want to fix the random number generation to a range. For instance, if you'd like to generate a 6 digit long random number, you'll want numbers from 100,000 to 999,999. You can achieve this by using the following formula.

Random r = new Random();
int randomNum = r.nextInt((max - min) + 1) + min;

Where max is the maximum number, such as 999999, and min is your minimum number, such as 100000.

EDIT:

Based on your comment, I see that you're trying to generate a 15-digit number containing only 1-5 inclusive. Here is a simple way to do this:

import java.util.Random;

StringBuilder s = new StringBuilder();
Random r = new Random();

for (int i = 0; i < 15; i++) {
    s.append(r.nextInt(5) + 1);
}

System.out.println("The random number is: " + s.toString());

As noted by @MichaelT, a 15 digit number will not fit in an integer. If you need to perform an operation on it, you should store it in a long.

long randomLong = Long.valueOf(s.toString()).longValue();

Upvotes: 3

Patricia Shanahan
Patricia Shanahan

Reputation: 26185

Rather than thinking of generating an integer, think in terms of generating a String of 15 digits, each in the required range.

You can use nextInt(int) to pick each digit.

Upvotes: 1

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