add parallel stream with side effect example

Author: mariofusco

src/main/java/lambdasinaction/chap6/ParallelStreams.java

@@ -27,4 +27,24 @@ public static long rangedSum(long n) {
     public static long parallelRangedSum(long n) {
         return LongStream.rangeClosed(1, n).parallel().reduce(Long::sum).getAsLong();
     }
+
+    public static long sideEffectSum(long n) {
+        Accumulator accumulator = new Accumulator();
+        LongStream.rangeClosed(1, n).forEach(accumulator::add);
+        return accumulator.total;
+    }
+
+    public static long sideEffectParallelSum(long n) {
+        Accumulator accumulator = new Accumulator();
+        LongStream.rangeClosed(1, n).parallel().forEach(accumulator::add);
+        return accumulator.total;
+    }
+
+    public static class Accumulator {
+        private long total = 0;
+
+        public void add(long value) {
+            total += value;
+        }
+    }
 }

src/main/java/lambdasinaction/chap6/ParallelStreamsHarness.java

@@ -14,6 +14,8 @@ public static void main(String[] args) {
         System.out.println("Range forkJoinSum done in: " + measurePerf(ParallelStreams::rangedSum, 10_000_000L) + " msecs");
         System.out.println("Parallel range forkJoinSum done in: " + measurePerf(ParallelStreams::parallelRangedSum, 10_000_000L) + " msecs" );
         System.out.println("ForkJoin sum done in: " + measurePerf(ForkJoinSumCalculator::forkJoinSum, 10_000_000L) + " msecs" );
+        System.out.println("SideEffect sum done in: " + measurePerf(ParallelStreams::sideEffectSum, 10_000_000L) + " msecs" );
+        System.out.println("SideEffect prallel sum done in: " + measurePerf(ParallelStreams::sideEffectParallelSum, 10_000_000L) + " msecs" );
     }
 
     public static <T, R> long measurePerf(Function<T, R> f, T input) {