Feature required in #73 (#77)

src/main/java/strman/Strman.java

@@ -34,6 +34,9 @@ import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Stream;
 
+import static java.util.function.Function.identity;
+import static java.util.stream.Collectors.counting;
+import static java.util.stream.Collectors.groupingBy;
 import static java.util.stream.Collectors.joining;
 
 /**
@@ -87,7 +90,7 @@ public abstract class Strman {
      * @return an Optional String if found else empty
      */
     public static Optional<String> at(final String value, int index) {
-        if (value == null || value.isEmpty()) {
+        if (isNullOrEmpty(value)) {
             return Optional.empty();
         }
         int length = value.length();
@@ -97,6 +100,10 @@ public abstract class Strman {
         return (index < length && index >= 0) ? Optional.of(String.valueOf(value.charAt(index))) : Optional.empty();
     }
 
+    private static boolean isNullOrEmpty(String input) {
+        return input == null || input.isEmpty();
+    }
+
     /**
      * Returns an array with strings between start and end.
      *
@@ -1302,4 +1309,20 @@ public abstract class Strman {
         }
         return countSubstr(value.substring(offset), subStr, allowOverlapping, ++count);
     }
+
+    /**
+     * Counts the number of occurrences of each character in the string
+     *
+     * @param input The input string
+     * @return A map containing the number of occurrences of each character in the string
+     */
+    public static Map<Character, Long> charsCount(String input) {
+        if (isNullOrEmpty(input)) {
+            return Collections.emptyMap();
+        }
+
+        return input.chars()
+                .mapToObj(c -> (char) c)
+                .collect(groupingBy(identity(), counting()));
+    }
 }

src/test/java/strman/StrmanTest.java

@@ -29,8 +29,7 @@ package strman;
 import org.junit.Ignore;
 import org.junit.Test;
 
-import java.util.Arrays;
-import java.util.Optional;
+import java.util.*;
 
 import static java.util.stream.Collectors.toList;
 import static org.hamcrest.CoreMatchers.*;
@@ -990,4 +989,42 @@ public class StrmanTest {
         assertThat(trimEnd("-_-abc!-_-", "_", "-", "!"), is(Optional.of("-_-abc")));
         assertThat(trimEnd("-_-abc#-_-", "_", "-", "!", "#"), is(Optional.of("-_-abc")));
     }
+
+
+    @Test
+    public void charsCount_shouldReturnEmptyWhenInputStringIsNull(){
+        assertThat(charsCount(null), equalTo(Collections.emptyMap()));
+    }
+
+    @Test
+    public void charsCount_shouldReturnEmptyWhenInputStringIsEmpty(){
+        assertThat(charsCount(""), equalTo(Collections.emptyMap()));
+    }
+
+    @Test
+    public void charsCount_shouldReturnCharsCountWhenInputIsASimpleString(){
+        Map<Character, Long> expectedOutput = new HashMap<Character, Long>(){{
+                put('a',1L);
+                put('b', 1L);
+                put('c', 1L);
+        }};
+
+        assertThat(charsCount("abc"), equalTo(expectedOutput));
+    }
+
+    @Test
+    public void charsCount_shouldReturnCharsCountWhenInputIsAComplexString(){
+        Map<Character, Long> expectedOutput = new HashMap<Character, Long>(){{
+            put('a',1L);
+            put('b', 2L);
+            put('c', 3L);
+
+            put('A',1L);
+            put('B', 2L);
+            put('C', 3L);
+            put('-', 10L);
+        }};
+
+        assertThat(charsCount("-----abbcccCCCBBA-----"), equalTo(expectedOutput));
+    }
 }