Code snippet from The Coding Café - Statistics.java

Statistics.java

class Statistics {
    int count = 0;
    int sum = 0;
    int min = Integer.MAX_VALUE;
    int max = Integer.MIN_VALUE;
    
    Statistics add(Integer value) {
        count++;                        // 1️⃣ Track how many elements
        sum += value;                   // 2️⃣ Running total
        min = Math.min(min, value);     // 3️⃣ Track minimum
        max = Math.max(max, value);     // 4️⃣ Track maximum
        return this;                    // 5️⃣ Return self for chaining
    }
    
    double getAverage() {
        return count == 0 ? 0 : (double) sum / count;
    }
}

Statistics stats = values.stream()
    .gather(Gatherers.fold(
        Statistics::new,       // 1️⃣ Create fresh Statistics object
        Statistics::add        // 2️⃣ Add each element to our statistics
    ))
    .findFirst()              // 3️⃣ Fold returns a single-element stream
    .orElse(new Statistics());

System.out.printf("Count: %d, Sum: %d, Avg: %.2f, Min: %d, Max: %d%n",
    stats.count, stats.sum, stats.getAverage(), stats.min, stats.max);
// Output: Count: 9, Sum: 45, Avg: 5.00, Min: 1, Max: 9