How to count and list odd numbers in an array

Question

public class OddsAndEvens {

    // counts all the odd numbers in the array
    private static int countOdds(int[] array) {
        int count = 0;

        for(int i = 0; i < array.length; i++) {
            if(array[i] % 2 == 1 && array[i] % 2 != 0) {
                count++;

            }
        }
        return count;

    }

    // returns an array with all the odd numbers
    public static int[] getAllOdds(int[] array) {
        int[] yaArray = new int[countOdds(array)];
        int j = 0;

        for(int i = 0; i < array.length; i++) {
            if(array[i] % 2 == 1 && array[i] % 2 != 0) {
                yaArray[j] = array[i];

            }
            j++;

        }
        return yaArray;

    }
}

///////////////////////////////////////////////////////////
runner code

public class OddsAndEvensRunner {

    public static void main(String args[]) {
        System.out.println("Odds - " + Arrays.toString(OddsAndEvens.getAllOdds(new int[]{2,4,6,8,10,12,14})));
        System.out.println("Evens - " + Arrays.toString(OddsAndEvens.getAllEvens(new int[]{2,4,6,8,10,12,14})));
        System.out.println("\nOdds - " + Arrays.toString(OddsAndEvens.getAllOdds(new int[]{1,2,3,4,5,6,7,8,9})));
        System.out.println("Evens - " + Arrays.toString(OddsAndEvens.getAllEvens(new int[]{1,2,3,4,5,6,7,8,9})));
        System.out.println("\nOdds - " + Arrays.toString(OddsAndEvens.getAllOdds(new int[]{2,10,20,21,23,24,40,55,60,61})));
        System.out.println("Evens - " + Arrays.toString(OddsAndEvens.getAllEvens(new int[]{2,10,20,21,23,24,40,55,60,61})));

    }
}

Ignore code relating to evens. When run the odd array only lists out one odd number instead of the others inside of the first array along with a couple of zeros. I tried a lot of things but simply won't count all of the odd numbers.

Answer 1

Take a look at this part:

public static int[] getAllOdds(int[] array) // when 
{
    int[] yaArray = new int[countOdds(array)];
    int j = 0;
    for(int i = 0; i<array.length;i++)
        if(array[i]%2==1 && array[i]%2!=0)
            yaArray[j]=array[i];
            j++;
    return yaArray;
}

The variable j is incremented only once, which is after the loop ends. If you have multiple statements to be executed in looping or conditional branch, use brackets.

Also array[i]%2==1 means the same thing as array[i]%2!=0 , so can eliminate one of them.

public static int[] getAllOdds(int[] array) // when 
{
    int[] yaArray = new int[countOdds(array)];
    int j = 0;
    for(int i = 0; i<array.length;i++)
    {
        if(array[i]%2==1)
        {
            yaArray[j]=array[i];
            j++;
        }
    }
    return yaArray;
}

Answer 2

Use List instead of Arrays. List is better to use.

Try like this,

public static void main(String[] args) {
    System.out.println("Odds - " + Arrays.toString(getAllEvens(new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 })));
    System.out.println("Evens - " + Arrays.toString(getAllOdds(new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 })));
}

public static Object[] getAllOdds(int[] array) {
    List<Integer> list = new ArrayList<>();
    for (int no : array) {
        if (no % 2 != 0)
            list.add(no);
    }
    return list.toArray();
}

public static Object[] getAllEvens(int[] array) {
    List<Integer> list = new ArrayList<>();
    for (int no : array) {
        if (no % 2 == 0)
            list.add(no);
    }
    return list.toArray();
}

You can also return list instead of list.toArray() for better list.