How to find the sum of numbers from an array in java?

In Java 8, you can use stream{[6 in 1 line]}

int myArray[] = {3, 5, 7, 12};
int total = IntStream.of(myArray).sum();

Similarly, you can use the class Arrays

Arrays.stream(myArray).sum() 

The stream method has overloads for primitive types and a generalized form, which is suitable for arrays of other types.

There are several ways to find the sum of elements in an array:

• Using the Java 8 Stream API (first using the method Arrays::stream convert the array to a stream of integers, then get the sum of this stream by the method Stream::sum)

  int array[] = {3, 5, 7, 12};
  int sum = Arrays.stream(array).sum();
  

• Cycle by elements (for-each cycle)

  int array[] = {3, 5, 7, 12};
  int sum = 0;
  for (int element : array)
      sum += element;
  

• Loop with using indexes

  int array[] = {3, 5, 7, 12};
  int sum = 0;
  for (int i = 0; i < array.length; ++i)
      sum += array[i];
  

Online code examples:

• Java 8 Stream API
• Cycle for-each
• Cycle by index

/**
 * Sum of all elements from 1 to 1000
 */
final int sum = Stream.iterate(1, n -> n + 1).limit(1000).mapToInt(el -> el).sum();

public class test {
    public static int[] myArray;
    public static void main(String[] args) {
        int myArray[] = {3, 5, 7, 12};
        System.out.print(sum(myArray));
    }
    public static int sum(int[] arr) {
        return sum(arr, 0, 0);
    }
    public static int sum(int[] arr, int sum, int count) {
        sum += arr[count];
        if (count < arr.length - 1) return sum(arr, sum, count + 1);
        return sum;
    }
}

for (int i = 0; i < arraySize; i++) {
    numbers[i] = numberOfArrayElements.nextInt();
    sum = sum + numbers[i];
}

Counting the sum of two numbers. If it is, we return TRUE:

public class moed2AQuation2A2015 {
    public static void main(String args[]) {
        int arr[] = {-2, 3, 5, 7, 12};
        System.out.println(sum2(arr, 19));
    }

    public static boolean sum2(int[] arr, int num) {
        return sum2(arr, num, 0, arr.length - 1);
    }

    public static boolean sum2(int[] arr, int n, int first, int second) {
        int summa = arr[first] + arr[second];
        if (summa == n) return true;
        if (second < first && first == second) return false;
        if (first < arr.length - 1 && second != first)
            return sum2(arr, n, first, second - 1) || sum2(arr, n, first + 1, second);
        else return false;
    }
}

/**
 * calculate sum of  the array
 */
public static void main(String[] args) {
    int myArray[] = {3, 5, 7, 12};
    System.out.print(sum(myArray));
}

public static int sum(int[] arr) {
    return sum(arr, arr.length - 1);
}

public static int sum(int[] arr, int n) {
    if (n == 0)
        return arr[0];
    else
        return arr[n] + sum(arr, n - 1);
}

Here are 3 ways, from the most primitive, to the normal. Don't criticize too much, I'm just learning.

import java.util.Arrays;

// сумма всех элементов массива, способ первый
class BlaBlaBla1 {
    public static void main(String[] args) {
        int[] nums = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        int sum = 0;

        for (int i = 0; i < nums.length; i++) sum += nums[i];
        System.out.println("1ый способ = " + sum);
    }
}

// сумма всех элементов массива, способ второй
class BlaBlaBla2 {
    public static void main(String[] args) {
        int[] nums = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        int sum = 0;

        sum = Arrays.stream(nums).sum();
        System.out.println("2ой способ = " + sum);
    }
}

// сумма всех элементов массива, способ третий: FOR-EACH
class BlaBlaBla3 {
    public static void main(String[] args) {
        int[] nums = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        int sum = 0;

        for (int x : nums) sum += x;
        System.out.println("3ий способ = " + sum);
    }
}