Sum of Array in Java: Solution, Explanation & Practice

Calculate the sum of array elements

Problem summary

Find the sum of all elements in the array [5, 10, 15, 20, 25].

Starter code

public class Main {
    public static void main(String[] args) {
        int[] numbers = {5, 10, 15, 20, 25};
        
        // Calculate and print sum
        // Print: Sum: <result>
    }
}

Expected output and test cases

Sum of array
```
Sum: 75
```

Hints

Initialize sum to 0
Add each element to sum
Use for-each or regular for loop

Validated solution

Reveal Java solution

public class Main {
    static int sum(int[] values) {
        int total = 0;
        for (int value : values) total += value;
        return total;
    }

    public static void main(String[] args) {
        int[] values = {5, 10, 15, 20, 25};
        System.out.println("Sum: " + sum(values));
    }
}

How to approach the problem

A running total is the smallest state needed. After each iteration it equals the sum of every value already visited, which makes the empty-array result naturally zero.

Approach

Start with the additive identity, zero.
Visit each element once.
Add the current value to the running total.

Time and space complexity

Time: O(n). Space: O(1).

Edge cases to test

An empty array has sum zero.
Many large ints can overflow int; promote total to long when required.

Common mistakes

Initializing total to the first element and then failing on empty input.
Using a nested loop and counting values repeatedly.

Follow-up challenge

Return both the sum and an overflow-safe average as a small result object.

Related Arrays exercises

Practice all Arrays exercises · Run this idea in the Java compiler