BAEL-3608: Add Map.merge() usage example (eugenp#8455)

kwoyke · pivovarit · commit 8c77986e6a4d · 2020-01-03T08:51:16.000+02:00
diff --git a/core-java-modules/core-java-collections-list-3/src/main/java/com/baeldung/list/duplicatescounter/DuplicatesCounter.java b/core-java-modules/core-java-collections-list-3/src/main/java/com/baeldung/list/duplicatescounter/DuplicatesCounter.java
@@ -24,11 +24,21 @@ public static <T> Map<T, Long> countByClassicalLoop(List<T> inputList) {
         return resultMap;
     }
 
-    public static <T> Map<T, Long> countByClassicalLoopWithMapCompute(List<T> inputList) {
+    public static <T> Map<T, Long> countByForEachLoopWithGetOrDefault(List<T> inputList) {
         Map<T, Long> resultMap = new HashMap<>();
-        for (T element : inputList) {
-            resultMap.compute(element, (k, v) -> v == null ? 1 : v + 1);
-        }
+        inputList.forEach(e -> resultMap.put(e, resultMap.getOrDefault(e, 0L) + 1L));
+        return resultMap;
+    }
+
+    public static <T> Map<T, Long> countByForEachLoopWithMapCompute(List<T> inputList) {
+        Map<T, Long> resultMap = new HashMap<>();
+        inputList.forEach(e -> resultMap.compute(e, (k, v) -> v == null ? 1L : v + 1L));
+        return resultMap;
+    }
+
+    public static <T> Map<T, Long> countByForEachLoopWithMapMerge(List<T> inputList) {
+        Map<T, Long> resultMap = new HashMap<>();
+        inputList.forEach(e -> resultMap.merge(e, 1L, Long::sum));
         return resultMap;
     }
 
diff --git a/core-java-modules/core-java-collections-list-3/src/test/java/com/baeldung/list/duplicatescounter/DuplicatesCounterUnitTest.java b/core-java-modules/core-java-collections-list-3/src/test/java/com/baeldung/list/duplicatescounter/DuplicatesCounterUnitTest.java
@@ -11,7 +11,6 @@
 
 class DuplicatesCounterUnitTest {
 
-
     private static List<String> INPUT_LIST = Lists.list(
         "expect1",
         "expect2", "expect2",
@@ -24,10 +23,21 @@ void givenInput_whenCountByClassicalLoop_thenGetResultMap() {
         verifyResult(result);
     }
 
+    @Test
+    void givenInput_whenCountByForEachLoopWithGetOrDefault_thenGetResultMap() {
+        Map<String, Long> result = DuplicatesCounter.countByForEachLoopWithGetOrDefault(INPUT_LIST);
+        verifyResult(result);
+    }
+
+    @Test
+    void givenInput_whenCountByForEachLoopWithMapCompute_thenGetResultMap() {
+        Map<String, Long> result = DuplicatesCounter.countByForEachLoopWithMapCompute(INPUT_LIST);
+        verifyResult(result);
+    }
 
     @Test
-    void givenInput_whenCountByClassicalLoopWithMapCompute_thenGetResultMap() {
-        Map<String, Long> result = DuplicatesCounter.countByClassicalLoopWithMapCompute(INPUT_LIST);
+    void givenInput_whenCountByForEachLoopWithMapMerge_thenGetResultMap() {
+        Map<String, Long> result = DuplicatesCounter.countByForEachLoopWithMapMerge(INPUT_LIST);
         verifyResult(result);
     }
 
