feat: Add most common interview question on java

JavaDsaWithTest/src/main/java/org/practice/dsa/java8/functional_programming/interview/DuplicateFromString.java

@@ -0,0 +1,29 @@
+package org.practice.dsa.java8.functional_programming.interview;
+
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+* Problem: Find Duplicate Characters in a String
+* Given a string, find all the duplicate characters and their counts using the Java 8 Stream API.
+* The result should be a Map<Character, Integer>.
+* */
+public class DuplicateFromString {
+    public static void main(String[] args) {
+        System.out.println(duplicate("programming"));
+    }
+
+    public static Map<Character, Long> duplicate(String input) {
+        return input.chars()
+                .mapToObj(c -> (char) c)
+                .collect(Collectors.groupingBy(
+                        c -> c, Collectors.counting()
+                )).entrySet()
+                .stream()
+                .filter(entry -> entry.getValue() > 1)
+                .collect(Collectors.toMap(
+                        Map.Entry::getKey,
+                        Map.Entry::getValue
+        ));
+    }
+}