Week 3: Objects, files and exceptions/13b. Draw lottery numbers

The following method definition is provided in the program:

ArrayList<Integer> lotterynumbers(Random r)

Write an implementation of the method that returns the lottery numbers in the list. 
There are seven numbers, ranging from [1, 39]. 
The same number cannot appear twice in the list.


Example method call:
public static void main(String[] args){
    Random rnd = new Random();
    System.out.println(lotterynumbers(r));
    System.out.println(lotterynumbers(r));
}

Example output:
[37, 14, 32, 20, 28, 21, 25]
[20, 6, 23, 30, 13, 11, 26]





==================================



import java.util.Random;
import java.util.ArrayList;
import java.util.HashSet;

public class Test{
    public static void main(String[] args){
        final Random r = new Random();
        
        
        System.out.println("Testing...");
        
        ArrayList<Integer> nrot1 = lotterynumbers(r);
        ArrayList<Integer> nrot2 = lotterynumbers(r);
        
        System.out.println("Numbers: " + nrot1);
        System.out.println("");
        


        // check 7 numbers
        System.out.print("Seven numbers in the list: ");
        System.out.println(nrot1.size() == 7 ? "Ok" : "No");
        



        // check 1-39
        boolean limit = true;
        for (int nro : nrot1) {
            if (nro < 1 || nro > 39) limit = false;
        }
        System.out.print("Numbers between 1 and 39: ");
        System.out.println(limit ? "Ok" : "No");



        // check unique
        HashSet<Integer> hs = new HashSet<>(nrot1);
        boolean same = hs.size() == 7;
        System.out.print("All numbers unique: ");
        System.out.println(same ? "Ok" : "No");
        

        // check both lists are different in content
        boolean diff = !(nrot1.equals(nrot2));
        System.out.print("Random numbers: ");
        System.out.println(diff ? "Ok" : "No");
        
        
        
    }



    // RETURN a list of 7 integers
    public static ArrayList<Integer> lotterynumbers(Random r) {
        ArrayList<Integer> numbers = new ArrayList<>();

        for (int i=0; i<7; i++) {
            // r.nextInt(39) => generates 0 to 38
            // +1 => adjusts the range to '1 to 39'
            int nro = r.nextInt(39) + 1;

            // check if number is unique - then add to the list
            if (!numbers.contains(nro)) {
                numbers.add(nro);
            }
            else {
                // adjust idx 'i' back by 1 to generate a new number through the loop
                i--;
            }
        }

        return numbers;

    }
    
}








Testing...
Numbers: [31, 4, 8, 3, 17, 32, 1]

Seven numbers in the list: Ok
Numbers between 1 and 39: Ok
All numbers unique: Ok
Random numbers: Ok