How to Sum a Mixed Array in Java

The challenge

Given an array of integers as strings and numbers, return the sum of the array values as if all were numbers.

Return your answer as a number.

The solution in Java code

Option 1 (using stream):

import java.util.List;

public class MixedSum {

  public int sum(List<?> mixed) {
    return mixed.stream().mapToInt(o -> Integer.parseInt(o.toString())).sum();
  }

}

Option 2 (the harder way):

import java.util.List;

public class MixedSum {
  public int sum(List<?> mixed) { 
      int sum = 0;
    
      for (Object element : mixed) {
        if (element instanceof Integer) {
          sum += (Integer) element;
        } else if (element instanceof String) {
          sum += Integer.parseInt( (String) element );
        }
      }
      return sum;
  }
}

Option 3 (using Objects):

import java.util.List;

public class MixedSum {

  public int sum(List<?> mixed) { 
  
    int x = 0;
    for(Object s: mixed){
            x+=Integer.parseInt(s.toString());
    }
    
    return x;  
  }
}

Test cases to validate our solution

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

import java.util.Arrays;

public class SolutionTest {
  
    MixedSum mixedSum = new MixedSum();

    @Test
    public void test_1() {
        assertEquals(10, mixedSum.sum(Arrays.asList(5,"5")));
    }
    
     @Test
    public void test_2() {
        assertEquals(22, mixedSum.sum(Arrays.asList(9, 3, "7", "3")));
    }
    
    @Test
    public void test_3() {
        assertEquals(42, mixedSum.sum(Arrays.asList("5", "0", 9, 3, 2, 1, "9", 6, 7)));
    }
    
    @Test
    public void test_4() {
        assertEquals(41, mixedSum.sum(Arrays.asList("3", 6, 6, 0, "5", 8, 5, "6", 2, "0")));
    }
    
    @Test
    public void test_5() {
        assertEquals(45, mixedSum.sum(Arrays.asList("1", "5", "8", 8, 9, 9, 2, "3")));
    }
    
    @Test
    public void test_6() {
        assertEquals(41, mixedSum.sum(Arrays.asList("3", 6, 6, 0, "5", 8, 5, "6", 2, "0")));
    }
    
    @Test
    public void test_7() {
        assertEquals(61, mixedSum.sum(Arrays.asList(8, 0, 0, 8, 5, 7, 2, 3, 7, 8, 6, 7)));
    }
}
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