BAEL-9260: Hashmap Implementation to Count the Occurrences of Each Ch… (#18599)

* BAEL-9260: Hashmap Implementation to Count the Occurrences of Each Character in Java

* BAEL-9260: Hashmap Implementation to Count the Occurrences of Each Character in Java

* BAEL-9260: Hashmap Implementation to Count the Occurrences of Each Character in Java

Author: achraftt

core-java-modules/core-java-string-algorithms-5/src/main/java/com/baeldung/countingchars/CharacterFrequencyCounter.java

@@ -0,0 +1,29 @@
+package com.baeldung.countingchars;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+public class CharacterFrequencyCounter {
+
+    public static Map<Character, Integer> countCharactersWithLoop(String input) {
+        Map<Character, Integer> characterCountMap = new HashMap<>();
+
+        for (char ch : input.toCharArray()) {
+            characterCountMap.put(ch, characterCountMap.getOrDefault(ch, 0) + 1);
+        }
+
+        return characterCountMap;
+    }
+
+    public static Map<Character, Integer> countCharactersWithStreams(String input) {
+        return input.chars()
+            .mapToObj(c -> (char) c)
+            .collect(Collectors.groupingBy(
+                Function.identity(),
+                Collectors.collectingAndThen(Collectors.counting(), Long::intValue)
+            ));
+    }
+
+}

core-java-modules/core-java-string-algorithms-5/src/test/java/com/baeldung/countingchars/CharacterFrequencyCounterUnitTest.java

@@ -0,0 +1,34 @@
+package com.baeldung.countingchars;
+
+import org.junit.Test;
+
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+
+public class CharacterFrequencyCounterUnitTest {
+
+    @Test
+    public void givenSimpleInput_whenCountingCharactersWithLoop_thenReturnsCorrectFrequencies() {
+        String input = "test";
+        Map<Character, Integer> result = CharacterFrequencyCounter.countCharactersWithLoop(input);
+
+        assertEquals(Integer.valueOf(2), result.get('t'));
+        assertEquals(Integer.valueOf(1), result.get('e'));
+        assertEquals(Integer.valueOf(1), result.get('s'));
+        assertEquals(3, result.size());
+    }
+
+    @Test
+    public void givenSimpleInput_whenCountingCharactersWithStreams_thenReturnsCorrectFrequencies() {
+        String input = "test";
+        Map<Character, Integer> result = CharacterFrequencyCounter.countCharactersWithStreams(input);
+
+        assertEquals(Integer.valueOf(2), result.get('t'));
+        assertEquals(Integer.valueOf(1), result.get('e'));
+        assertEquals(Integer.valueOf(1), result.get('s'));
+        assertEquals(3, result.size());
+    }
+
+
+}