Output of odd array elements separated by commas Java

Please help me, how can I remove the comma at the end?

Why are you adding it?

stringBuilder.append(arr[i] + ",");

For each element, a comma is added at the end. There are three solutions here

1. After the loop, remove the last comma from StringBuilder

   if (stringBuilder.length() > 0)
     stringBuilder.deleteCharAt(stringBuilder.length() - 1)
   

2. Add a comma before the element for all but the first

   if (stringBuilder.length() > 0)
     stringBuilder.append(',');
   stringBuilder.append(arr[i]);
   

3. Add the desired items to the list, and then call Arrays.toString(tmpList)

This code does not work if the array elements are negative

Because the remainder of dividing a negative odd number by 2 will be -1. So if the odd check is rewritten like this

if (arr[i] % 2 != 0)

Then the code will work with both positive and negative numbers

In addition, with such a cycle

for (int i = 0; i < arr.length - 1; i++) {

You will skip the last element of the array. The loop should be like this

for (int i = 0; i < arr.length; i++) {

There is an interesting StringJoiner class for such things.

Here is an example:

public static void main(String[] args) {
    StringJoiner joiner = new StringJoiner(",", "", "\r\n");
    int[] arr = {3,5,20,8,7,3,100};
    for (int e : arr) {
        if (e % 2 != 0)
            joiner.add(String.valueOf(e));
    }
    System.out.println(joiner.toString());
}

string.substring(0,string.length() -1)

Your loop exit condition is incorrect

 i < arr.length - 1

The unit does not need to be subtracted, because of this, the last element of the array is not analyzed at all. You need to do this:

i < arr.length

This line is generally superfluous, since it essentially does nothing, and the line feed does System.out.println

stringBuilder.append(System.getProperty("line.separator"));

The comma condition is incorrect, as it will only work if you have the last element odd. It is more logical in this case to put a comma before the number, and not after it. For negative ones, take the module from the remainder. The result will be something like this:

public static void printOddNumbers(int[] arr) {
    StringBuilder stringBuilder = new StringBuilder();
    boolean first = true;
    for (int i = 0; i < arr.length; i++) {
        if (Math.abs(arr[i] % 2) == 1)
            if (first) {
                stringBuilder.append(arr[i]);
                first = false;
            } else {
                stringBuilder.append("," + arr[i]);
            }
    }
    System.out.println(stringBuilder);
}

Well, the streams why no one offered

int[] strArray = new int[]{3, 5, 20, 8, 7, 3, 100};
String result = IntStream.of(strArray)
        .filter(i -> (i & 1) != 0)
        .mapToObj(String::valueOf)
        .collect(Collectors.joining(","));
System.out.println(result);

Method Stream.flatMap allows you to expand the current stream with additional elements:

public static void main(String[] args) {
    printOddNumbers(new int[]{3, 5, 20, 8, 7, 3, 100}); // 3,5,7,3
}

public static void printOddNumbers(int[] arr) {
    Arrays.stream(arr)
            // нечетные числа
            .filter(i -> i % 2 != 0)
            // число в виде строки
            .mapToObj(String::valueOf)
            // добавляем запятую перед
            // каждой строкой
            .flatMap(i -> Stream.of(",", i))
            // пропускаем первую запятую
            .skip(1)
            // выводим в одну строку
            .forEach(System.out::print);
    // перевод курсора
    // на новую строку
    System.out.println();
}