Adding reduce() stream operations

spdpiyush · spdpiyush · commit 7cd390980b35 · 2025-02-27T13:35:26.000+05:30
diff --git a/Modern-Java-Examples/src/com/learn/streams/StreamsReduceExample.java b/Modern-Java-Examples/src/com/learn/streams/StreamsReduceExample.java
@@ -0,0 +1,45 @@
+package com.learn.streams;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+public class StreamsReduceExample {
+
+    public static void main(String[] args) {
+
+        List<Integer> numbers = List.of(10, 20, 30, 40);
+        System.out.println(performMultiplication(numbers));
+
+        Optional<Integer> result1 = perfromMultiplicationWithoutIdentity(numbers);
+        System.out.println(result1.isPresent());
+        System.out.println(result1.get());
+
+        Optional<Integer> result2 = perfromMultiplicationWithoutIdentity(new ArrayList<>());
+        System.out.println(result2.isPresent());
+
+    }
+
+    /**
+     * <p>
+     *     Preform multiplication of the list.
+     * </p>
+     * @param integerList
+     * @return
+     */
+    public static int performMultiplication(List<Integer> integerList) {
+
+        return integerList.stream()
+                // num1 = 1 num2 = 10 (from Stream) => 1 * 10 result returned
+                // num1 = 10, num2 = 20 (from Stream) => 10 * 20 result returned
+                // num1 = 200 , num2 = 30 (from Stream) => 200 * 30 result returned
+                // num1 = 6000 , num2 = 40 (from Stream) => 24000 result returned
+                .reduce(1, (num1 , num2) -> num1 * num2);
+    }
+
+    public static Optional<Integer> perfromMultiplicationWithoutIdentity(List<Integer> integerList) {
+
+        return integerList.stream()
+                .reduce((num1, num2) -> num1 * num2);
+    }
+}
diff --git a/README.md b/README.md
@@ -30,6 +30,7 @@ This repository contains the basic &amp; advance level examples related to Java
     * [distinct(), count() and sorted()](Modern-Java-Examples/src/com/learn/streams/StreamsFlatMapExample.java)
     * [sort() using Comparator](Modern-Java-Examples/src/com/learn/streams/StreamsComparatorExample.java)
     * [filter()](Modern-Java-Examples/src/com/learn/streams/StreamsFilterExample.java)
+    * [reduct()](Modern-Java-Examples/src/com/learn/streams/StreamsReduceExample.java)
 
 
 
