Calculate averages from an int array in Java

The challenge

Write function avg which calculates average of numbers in given list.

The solution in Java code

Option 1 (working through the problem):

public class Solution {
  public static double find_average(int[] array){
    double sum = 0;
    
    for(int i=0; i<array.length; i++) {
      sum+=array[i];
    }
    
    return sum/array.length;
  }
}

Option 2 (using streams):

import java.util.Arrays;
public class Solution {
  public static double find_average(int[] array){
    return Arrays.stream(array).average().orElse(0);
  }
}

Option 3 (using an IntStream):

import java.util.stream.IntStream;

public class Solution {
  public static double find_average(int[] array){
    return IntStream.of(array).average().getAsDouble();
  }
}

Option 4 (an alternate IntStream approach):

import java.util.stream.IntStream;

public class Solution {
  public static double find_average(int[] array){
    return  IntStream.of(array).sum() / (double) array.length;
  }
}

Test cases to validate our solution

import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;

public class SolutionTest {

    private static final double DELTA = 1e-15;

    @Test
    public void testSomething() {
        assertEquals(1, Solution.find_average(new int[]{1,1,1}), DELTA);
        assertEquals(2, Solution.find_average(new int[]{1, 2, 3}), DELTA);
        assertEquals(2.5, Solution.find_average(new int[]{1, 2, 3, 4}), DELTA);
        
        System.out.println("Running 20 random tests...");
        
        for(int i=0; i<20; i++){
          int[] arr = randArray();
          assertEquals(solution(arr), Solution.find_average(arr), DELTA);
        }
    }
    
    private static int[] randArray(){
      int size = (int)Math.floor(Math.random()*5 + 2);
      int[] arr = new int[size];
      for(int i=0; i<size; i++){
        arr[i] = (int)Math.floor(Math.random()*20 + 1);
      }
      return arr;
    }
    
    private static double solution(int[] arr){
      int sum = 0;
      for(int i=0; i<arr.length; i++){
        sum += arr[i];
      }
      return (sum + 0.0) / arr.length;
    }
}