Add reduce examples

winterbe · winterbe · commit 4d556bddc3be · 2014-07-22T08:21:30.000+02:00
diff --git a/src/com/winterbe/java8/Streams11.java b/src/com/winterbe/java8/Streams11.java
@@ -0,0 +1,100 @@
+package com.winterbe.java8;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * @author Benjamin Winterberg
+ */
+public class Streams11 {
+
+    static class Person {
+        String name;
+        int age;
+
+        Person(String name, int age) {
+            this.name = name;
+            this.age = age;
+        }
+
+        @Override
+        public String toString() {
+            return name;
+        }
+    }
+
+    public static void main(String[] args) {
+        List<Person> persons =
+            Arrays.asList(
+                new Person("Max", 18),
+                new Person("Peter", 23),
+                new Person("Pamela", 23),
+                new Person("David", 12));
+
+//        test1(persons);
+//        test2(persons);
+//        test3(persons);
+//        test4(persons);
+        test5(persons);
+    }
+
+    private static void test1(List<Person> persons) {
+        persons
+            .stream()
+            .reduce((p1, p2) -> p1.age > p2.age ? p1 : p2)
+            .ifPresent(System.out::println);    // Pamela
+    }
+
+    private static void test2(List<Person> persons) {
+        Person result =
+            persons
+                .stream()
+                .reduce(new Person("", 0), (p1, p2) -> {
+                    p1.age += p2.age;
+                    p1.name += p2.name;
+                    return p1;
+                });
+
+        System.out.format("name=%s; age=%s", result.name, result.age);
+    }
+
+    private static void test3(List<Person> persons) {
+        Integer ageSum = persons
+            .stream()
+            .reduce(0, (sum, p) -> sum += p.age, (sum1, sum2) -> sum1 + sum2);
+
+        System.out.println(ageSum);
+    }
+
+    private static void test4(List<Person> persons) {
+        Integer ageSum = persons
+            .stream()
+            .reduce(0,
+                (sum, p) -> {
+                    System.out.format("accumulator: sum=%s; person=%s\n", sum, p);
+                    return sum += p.age;
+                },
+                (sum1, sum2) -> {
+                    System.out.format("combiner: sum1=%s; sum2=%s\n", sum1, sum2);
+                    return sum1 + sum2;
+                });
+
+        System.out.println(ageSum);
+    }
+
+    private static void test5(List<Person> persons) {
+        Integer ageSum = persons
+            .parallelStream()
+            .reduce(0,
+                (sum, p) -> {
+                    System.out.format("accumulator: sum=%s; person=%s\n", sum, p);
+                    return sum += p.age;
+                },
+                (sum1, sum2) -> {
+                    System.out.format("combiner: sum1=%s; sum2=%s\n", sum1, sum2);
+                    return sum1 + sum2;
+                });
+
+        System.out.println(ageSum);
+    }
+}
