Add examples of using collectors summarizing

aplotnikov · aplotnikov · commit fa07a12ea7a9 · 2018-12-26T19:25:27.000+01:00
diff --git a/src/main/java/io/github/aplotnikov/java_8_misuses/stream/collectors/StatisticsCalculation.java b/src/main/java/io/github/aplotnikov/java_8_misuses/stream/collectors/StatisticsCalculation.java
@@ -0,0 +1,40 @@
+package io.github.aplotnikov.java_8_misuses.stream.collectors;
+
+import io.github.aplotnikov.java_8_misuses.domain.Client;
+
+import java.util.IntSummaryStatistics;
+import java.util.List;
+import java.util.stream.IntStream;
+
+import static io.github.aplotnikov.java_8_misuses.utils.Annotations.Good;
+import static io.github.aplotnikov.java_8_misuses.utils.Annotations.Ugly;
+import static java.util.stream.Collectors.summarizingInt;
+
+class StatisticsCalculation {
+
+    @Ugly
+    class IterateThroughValuesSeveralTimes {
+        void findMinAndMaxClientAge(List<Client> clients) {
+            getClientAgesStream(clients)
+                    .max()
+                    .ifPresent(max -> System.out.println("MAX: " + max));
+
+            getClientAgesStream(clients)
+                    .min()
+                    .ifPresent(min -> System.out.println("MIN: " + min));
+        }
+
+        private IntStream getClientAgesStream(List<Client> clients) {
+            return clients.stream().mapToInt(Client::getAge);
+        }
+    }
+
+    @Good
+    class CalculateStatisticsInSingleRunWithCollector {
+        void findMinAndMaxClientAge(List<Client> clients) {
+            IntSummaryStatistics statistics = clients.stream().collect(summarizingInt(Client::getAge));
+            System.out.println("MAX: " + statistics.getMax());
+            System.out.println("MIN: " + statistics.getMin());
+        }
+    }
+}
