How to Sum a List of Integers Using Java Streams (Java 8+)

You can calculate the sum of integers in a list using the Stream API in several clean ways.

1- Best & Most Common Way

import java.util.Arrays;
import java.util.List;

public class Test1 {
	public static void main(String[] args) {
		List<Integer> numbers = Arrays.asList(1, 2, 3, 4);
		int sum = numbers.stream().mapToInt(Integer::intValue).sum();
		System.out.println("Sum: "+ sum);
	}
}

Output: Sum: 10

2- Using summaryStatistics() (for extra stats)

import java.util.Arrays;
import java.util.IntSummaryStatistics;
import java.util.List;

public class Test1 {
	public static void main(String[] args) {
		List<Integer> numbers = Arrays.asList(1, 2, 3, 4);
		IntSummaryStatistics stats = numbers.stream()
				.mapToInt(Integer::intValue).summaryStatistics();
		System.out.println("Sum: " + stats.getSum());
	}
}

Also gives getAverage(), getMin(), getMax()

Quick Comparison

Method	When to Use	Example
mapToInt().sum()	✅ Best for sum only	numbers.stream().mapToInt(Integer::intValue).sum();
summaryStatistics()	When you need more than sum like min, max	mapToInt(…).summaryStatistics().getSum();