How to create a method for finding the sum of array elements in Java and call it on different arrays?

Question

Java

In the problem of counting the queue service time from an arbitrary client at N cash desks, the queue is specified by an array of integers int[] customers, where each element customers[i] is the service time of the i-th client.
In the process of solving, it was necessary to sum the elements of the array in the case when we have N=1:

.........
        } else if (n == 1) {
            for (int i = 0; i < customers.length; i++ ) {
              sum += customers[i];
            }
        }
.........
return sum;

However, during the solution, it was necessary to find the sums of elements in two more arrays - nCustomers and restOfCustomers.
I'm creating a method that allows you to sum the elements of an arbitrary array:

public int sumOfArray(int ary[]) {
    int s = 0;
      for (int i = 0; i < ary.length; i++) {
        s += ary[i];
      }
      return s;
  }

How can I now syntactically correctly call it on all three arrays in the code - customers, nCustomers and restOfCustomers?

Answer 1

If I understand correctly and you need the sum of the elements of three arrays, then:
Or you can create a method with varargs that will calculate the sum of an arbitrary number of arrays:

public int sumOfArray(int[]... ary) {
        /// your code
    }

Or count through streams:

int sumOfAll = IntStream.of(arr1).sum() + IntStream.of(arr2).sum() + IntStream.of(arr3).sum();

Answer 2

I do this now

List<String> list  = new ArrayList<>();
    list.add("1");
    list.add("2");
    list.add("4");
    list.add("1");
    
    int summ = list.stream()
        .map(s -> Integer.parseInt(s)) // перевод из String в int
        .reduce( (s1,s2) ->  s1 + s2 ) // сумма
        .orElse(0); // значение по умолчанию
    System.out.println(summ);

Instead of list - use your collection of objects.
And inside map(....) take the desired field value.
ZYYU If with objects, then this is how you can

public class Reduce {
  public static class Offer {
    int price;
    public Offer (int price) {
      this.price = price;
    }
    
    public int getPrice() {
      return price;
    }
  }
  public static void main(String args[]) {
    List< Offer > list  = new ArrayList<>();
    list.add(new Offer(1));
    list.add(new Offer(2));
    list.add(new Offer(4));
    list.add(new Offer(1));
    
    int summ = list.stream()
        .map(Offer::getPrice) // взять прайс
        .reduce( (s1,s2) ->  s1 + s2 ) // сумма
        .orElse(0); // значение по умолчанию
    
    System.out.println(summ);
  }
}