Create tester program to record the frequency of rolls on a die?

Question

I need to make a class that has a public method roll() which will return a random int between 1 and 6. Then I need to make a tester program that measures the frequency of rolls meaning it counts up how many ones, twos, threes, etc. in 1000 rolls.

My die class is as below:

import java.util.Random;

public class Die {

  public int roll() {
    Random rand = new Random();
    int n = rand.nextInt(6) + 1;
    return n;
  }
}

and this is my tester class:

public class DieTester extends Die {
  public static void main(String[] args) {
    int ones = 0;
    int twos = 0;
    int threes = 0;
    int fours = 0;
    int fives = 0;
    int sixes = 0;

    for(int i = 0; i < 1000; i++) {
      int roll();
      if(n == 1) {
        ones = ones + 1;
      }
      if(n == 2) {
        twos = twos + 1;
      }
      if(n == 3) {
        threes = threes + 1;
      }
      if(n == 4) {
        fours = fours + 1;
      }
      if(n == 5) {
        fives = fives + 1;
      }
      if(n == 6) {
        sixes = sixes + 1;
      }
    }

    System.out.println(ones);
    System.out.println(twos);
    System.out.println(threes);
    System.out.println(fours);
    System.out.println(fives);
    System.out.println(sixes);
  }
}

However the int roll(); function in the Die Tester class is not working. How can I fix this?

Answer 1

luk2302's answer is correct. I think is worth to mention that you can do this a lot easier with Random::ints:

Map<Integer, Long> dieTest = new Random().ints(1000,1,7) // generate 1000 pseudorandom values from 1 to 6
        .boxed()                                         // box each int to Integer
        .collect(Collectors.groupingBy(Function.identity(), Collectors.counting())); // group by each distinct value counting the number of its occurrence in the stream

System.out.println(dieTest);

Sample output showing the frequency of each number:

{1=178, 2=158, 3=165, 4=154, 5=183, 6=162}

Answer 2

You have two issues:

• int roll(); is not a valid statement in its current place
• if you want to keep roll the way it is you need to create an instance of Die first, otherwise make it static

---

Solution using static

public class Die {
    public static int roll() {
        Random rand = new Random();
        int n = rand.nextInt(6) + 1;
        return n;
    }
}

public class DieTester {
    public static void main(String[] args) {
        // variables

        for(int i = 0; i < 1000; i++) {
            int n = Die.roll();
            // your if logic
        }

        // printing
    }
}

---

Solution using an instance of Die

public class Die {
    public int roll() {
        Random rand = new Random();
        int n = rand.nextInt(6) + 1;
        return n;
    }
}

public class DieTester {
    public static void main(String[] args) {
        // variables
        Die die = new Die();

        for(int i = 0; i < 1000; i++) {
            int n = die.roll();
            // your if logic
        }

        // printing
    }
}

---

In both cases it does not make much sense to make DieTester extend Die.