java 32 lines · 5 steps

Aggregating stats with IntSummaryStatistics

How a single stream pass collects count, min, max, sum, and average from a list of orders.

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Intermediate streams aggregation records method-reference

1import java.util.List;
2import java.util.IntSummaryStatistics;
3 
4public class OrderReport {
5 
6    public record Order(String customer, int itemCount, double total) {}
7 
8    public String summarizeItemCounts(List<Order> orders) {
9        IntSummaryStatistics stats = orders.stream()
10                .mapToInt(Order::itemCount)
11                .summaryStatistics();
12 
13        if (stats.getCount() == 0) {
14            return "No orders to report.";
15        }
16 
17        return String.format(
18                "Orders: %d | items min=%d, max=%d, sum=%d, avg=%.2f",
19                stats.getCount(),
20                stats.getMin(),
21                stats.getMax(),
22                stats.getSum(),
23                stats.getAverage());
24    }
25 
26    public boolean hasBulkOrder(List<Order> orders, int threshold) {
27        return orders.stream()
28                .mapToInt(Order::itemCount)
29                .summaryStatistics()
30                .getMax() >= threshold;
31    }
32}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1IntSummaryStatistics gathers count, min, max, sum, and average in one stream traversal.
2Guarding against an empty stream avoids meaningless zero or infinity results before formatting.
3Method references like Order::itemCount turn a record accessor into a clean projection for mapToInt.

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