How do you find the sum of all the numbers in an array in Java?

Question

I'm having a problem finding the sum of all of the integers in an array in Java. I cannot find any useful method in the Math class for this.

Answer 1

In java-8 you can use streams:

int[] a = {10,20,30,40,50}; int sum = IntStream.of(a).sum(); System.out.println("The sum is " + sum); 

Output:

The sum is 150.

It's in the package java.util.stream

import java.util.stream.*; 

Answer 2

If you're using Java 8, the Arrays class provides a stream(int[] array) method which returns a sequential IntStream with the specified int array. It has also been overloaded for double and long arrays.

int [] arr = {1,2,3,4}; int sum = Arrays.stream(arr).sum(); //prints 10 

It also provides a method stream(int[] array, int startInclusive, int endExclusive) which permits you to take a specified range of the array (which can be useful) :

int sum = Arrays.stream(new int []{1,2,3,4}, 0, 2).sum(); //prints 3 

Finally, it can take an array of type T. So you can per example have a String which contains numbers as an input and if you want to sum them just do :

int sum = Arrays.stream("1 2 3 4".split("\\s+")).mapToInt(Integer::parseInt).sum();