How to Find Array Average in Java

The Challenge

Calculate the average (mean) of all elements in an array!

Solutions

Method 1: Using Loop

java

int[] numbers = {10, 20, 30, 40, 50};
int sum = 0;

for (int num : numbers) {
    sum += num;
}

double average = (double) sum / numbers.length;
System.out.println("Average: " + average);
// Output: Average: 30.0

Method 2: Using Java 8 Streams

java

import java.util.Arrays;

int[] numbers = {10, 20, 30, 40, 50};
double average = Arrays.stream(numbers).average().orElse(0.0);

System.out.println("Average: " + average);
// Output: Average: 30.0

Did You Know?

The average() method returns an OptionalDouble to handle empty arrays gracefully. Use orElse() to provide a default value!

Watch Out!

Remember to cast to double to avoid integer division: (double) sum / length

Real-World Use Cases

Statistics: Calculate mean of dataset
Grading: Calculate student average
Analytics: Average user engagement
Performance: Average response time

›Short versionOpen if you only have a minute.

Average is the sum divided by the length.
int division drops the fraction. 3 / 2 is 1.
Cast before dividing: (double) sum / length.
An empty array has length 0. Do not divide.

Array average

Compute the total divided by the number of elements, keeping a fractional result.

Working approach

Sum in a long.
Reject an empty array.
Divide a double by the length.

Walk the sample

Values 2, 4, 7
Sum 13, length 3
13.0 / 3 is about 4.333

The trap

sum / length uses integer division whenever both sides are integral types, even if the variable you assign to is a double. The fraction is already gone.

java

static double average(int[] values) {
    if (values.length == 0) {
        throw new IllegalArgumentException("empty array");
    }
    long sum = 0;
    for (int value : values) {
        sum += value;
    }
    return (double) sum / values.length;
}

What is the average of {1, 2} if the sum and the length are both ints?

The sum is 3. 3 / 2 in int arithmetic is 1. Assigning 1 to a double stores 1.0.

(double) sum / length is 1.5. Check length before the division so an empty array does not throw ArithmeticException by accident.

Time O(n), space O(1).

Easy to get wrong

Dividing two ints and storing the truncated result in a double.
Dividing by length without checking for 0.