Generating random number in Java

Question

This is the question i got and how can i limit it to a range ? My code is below. Thanks

Question : Write a method call genRandom() to generate 5 Random integer numbers between 1 to 100 and print them on to the screen. Invoke genRandom() inside the main().

import java.util.Random;

class RandomNumbers{
    public static void main(String [] args){

        Random randomNum = new Random();

        for(int i = 0; i<5; i++){
            System.out.println("Random number is : " + randomNum.nextInt(5));
            }
    }
}

score 4 · Accepted Answer · edited Jul 13 '13 at 10:38

4

use 100 as argument in nextInt()

nextInt(100)

Update based on your comment

just create a new static method

public static int genRandom(){
  return new Random().nextInt(100);// or may be cache random instance
}

edited Jul 13 '13 at 10:38

Srivathsan

519
4
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answered Oct 14 '12 at 06:30

jmj

237,923
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It says Invoke genRandom() inside the main(). how to do this ? – ŦhųLẩnå FệrñảnDö Oct 14 '12 at 06:31
could you please elaborate it little more ? – jmj Oct 14 '12 at 06:35
Thanks for your time friend. The question says this " Write a method call genRandom() to generate 5 Random integer numbers between 1 to 100 and print them on to the screen. Invoke genRandom() inside the main()." But i think i havent written a method called getRandom() – ŦhųLẩnå FệrñảnDö Oct 14 '12 at 06:36
@ThuLana FernanDo, it is porbably related with your other problem. otherwise, it would just work fine if you replace your '5' inside nextInt() with '100' – Jimmy Oct 14 '12 at 06:37

score 1 · Answer 2 · answered Oct 14 '12 at 06:41

Write genRandom() in your RandomNumbers class and use as below:

    public class RandomNumbers{
       static Random randomNum = new Random();

       public static void main(String[] args){
          for(int i=0; i< 5; i++){
               System.out.println("Random number is : " + genRandom());
          }
       }

       public static int genRandom(){
          return randomNum.nextInt(100);
       }   
    }

score 0 · Answer 3 · answered Oct 14 '12 at 06:35

nextInt generates random number between 0 to your given range value . If you give 5 it will generates random between the 5 . If you want random numbers between 1 to 100 you will give 100 in nextInt method .

Please read the java 6 api documentation http://docs.oracle.com/javase/6/docs/api/java/util/Random.html#nextInt(int) .

score 0 · Answer 4 · answered Oct 14 '12 at 07:13

You can try something like this:

package com.stackoverflow.works;

import java.util.Random;

public class RandomNumber {

    public static int genRandom(int randomRange) {
        return new Random().nextInt(randomRange);
    }

    public static void genRandom(int randomRange, int displayCount) {
        for (int i = 0; i < displayCount; i++) {
            System.out.println("Random Number [Iteration " + (i + 1) +"]: " + genRandom(randomRange));
        }
    }

    public static void main(String[] args) {
        int randomRange = 100; // You can change the limit if required
        int displayCount = 5; // You can decide the iteration count

        RandomNumber.genRandom(randomRange, displayCount);
    }

}

Output:

Random Number [Iteration 1]: 14
Random Number [Iteration 2]: 84
Random Number [Iteration 3]: 96
Random Number [Iteration 4]: 38
Random Number [Iteration 5]: 61

techfoobar · Answer 5 · 2012-10-14T06:40:45.557

You can use nextDouble() like below:

r = minValue + ((new Random()).nextDouble() * (maxValue - minValue));

where minValue, maxValue is the range you want your random number in.

Full Code

import java.util.Random;

class Main {

    int genRandom(int minValue, int maxValue) {
        return (int) (minValue + ((new Random()).nextDouble() * (maxValue - minValue)));
    }

    public static void main(String [] args){
        Main m = new Main();
        for(int i = 0; i<5; i++){
            System.out.println("Random Number is: " + m.genRandom(1, 100));
        }
    }
}

Sample Output:

Random Number is: 95
Random Number is: 89
Random Number is: 9
Random Number is: 73
Random Number is: 20

Generating random number in Java

5 Answers5