diff --git a/kotlin/src/main/java/com/baeldung/java/StringUtils.java b/kotlin/src/main/java/com/baeldung/java/StringUtils.java
new file mode 100644
index 0000000000..f405924cdf
--- /dev/null
+++ b/kotlin/src/main/java/com/baeldung/java/StringUtils.java
@@ -0,0 +1,7 @@
+package com.baeldung.java;
+
+public class StringUtils {
+    public static String toUpperCase(String name) {
+        return name.toUpperCase();
+    }
+}
diff --git a/kotlin/src/main/kotlin/com/baeldung/kotlin/ItemService.kt b/kotlin/src/main/kotlin/com/baeldung/kotlin/ItemService.kt
index 3c0d2eacb1..88de1aa9be 100644
--- a/kotlin/src/main/kotlin/com/baeldung/kotlin/ItemService.kt
+++ b/kotlin/src/main/kotlin/com/baeldung/kotlin/ItemService.kt
@@ -24,29 +24,41 @@ class ItemManager(val categoryId: String, val dbConnection: String) {
     fun makeAnalyisOfCategory(catId: String): Unit {
         val result = if (catId == "100") "Yes" else "No"
         println(result)
-
+        `object`()
     }
+
+    fun sum(a: Int, b: Int): Int {
+        return a + b
+    }
+
+    fun `object`(): String {
+        return "this is object"
+    }
+
 }
 
 fun main(args: Array<String>) {
     val numbers = arrayOf("first", "second", "third", "fourth")
 
-    var concat = ""
     for (n in numbers) {
-        concat += n
+        println(n)
     }
 
-    var sum = 0
-    for (i in 2..9) {
-        sum += i
+    for (i in 2..9 step 2) {
+        println(i)
     }
 
+    val res = 1.rangeTo(10).map { it * 2 }
+    println(res)
+
     val firstName = "Tom"
     val secondName = "Mary"
     val concatOfNames = "$firstName + $secondName"
     println("Names: $concatOfNames")
+    val sum = "four: ${2 + 2}"
 
     val itemManager = ItemManager("cat_id", "db://connection")
+    ItemManager(categoryId = "catId", dbConnection = "db://Connection")
     val result = "function result: ${itemManager.isFromSpecificCategory("1")}"
     println(result)
 
@@ -63,4 +75,9 @@ fun main(args: Array<String>) {
         "Alice" -> println("Hi lady")
     }
 
+    val items = listOf(1, 2, 3, 4)
+
+
+    val rwList = mutableListOf(1, 2, 3)
+    rwList.add(5)
 }
\ No newline at end of file
diff --git a/kotlin/src/main/kotlin/com/baeldung/kotlin/MathematicsOperations.kt b/kotlin/src/main/kotlin/com/baeldung/kotlin/MathematicsOperations.kt
new file mode 100644
index 0000000000..924f9d2323
--- /dev/null
+++ b/kotlin/src/main/kotlin/com/baeldung/kotlin/MathematicsOperations.kt
@@ -0,0 +1,7 @@
+package com.baeldung.kotlin
+
+class MathematicsOperations {
+    fun addTwoNumbers(a: Int, b: Int): Int {
+        return a + b
+    }
+}
\ No newline at end of file
diff --git a/kotlin/src/test/java/com/baeldung/kotlin/JavaCallToKotlinTest.java b/kotlin/src/test/java/com/baeldung/kotlin/JavaCallToKotlinTest.java
new file mode 100644
index 0000000000..cfad7cefd4
--- /dev/null
+++ b/kotlin/src/test/java/com/baeldung/kotlin/JavaCallToKotlinTest.java
@@ -0,0 +1,17 @@
+package com.baeldung.kotlin;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class JavaCallToKotlinTest {
+    @Test
+    public void givenKotlinClass_whenCallFromJava_shouldProduceResults() {
+        //when
+        int res = new MathematicsOperations().addTwoNumbers(2, 4);
+
+        //then
+        assertEquals(6, res);
+
+    }
+}
diff --git a/kotlin/src/test/kotlin/com/baeldung/kotlin/KotlinScalaInteroperabilityTest.kt b/kotlin/src/test/kotlin/com/baeldung/kotlin/KotlinScalaInteroperabilityTest.kt
new file mode 100644
index 0000000000..f671c3af8b
--- /dev/null
+++ b/kotlin/src/test/kotlin/com/baeldung/kotlin/KotlinScalaInteroperabilityTest.kt
@@ -0,0 +1,20 @@
+package com.baeldung.kotlin
+
+import com.baeldung.java.StringUtils
+import org.junit.Test
+import kotlin.test.assertEquals
+
+
+class KotlinScalaInteroperabilityTest {
+    @Test
+    fun givenLowercaseString_whenExecuteMethodFromJavaStringUtils_shouldReturnStringUppercase() {
+        //given
+        val name = "tom"
+
+        //when
+        val res = StringUtils.toUpperCase(name)
+
+        //then
+        assertEquals(res, "TOM")
+    }
+}
diff --git a/kotlin/src/test/kotlin/com/baeldung/kotlin/LambdaTest.kt b/kotlin/src/test/kotlin/com/baeldung/kotlin/LambdaTest.kt
new file mode 100644
index 0000000000..34217336a0
--- /dev/null
+++ b/kotlin/src/test/kotlin/com/baeldung/kotlin/LambdaTest.kt
@@ -0,0 +1,19 @@
+package com.baeldung.kotlin
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+
+class LambdaTest {
+    @Test
+    fun givenListOfNumber_whenDoingOperationsUsingLambda_shouldReturnProperResult() {
+        //given
+        val listOfNumbers = listOf(1, 2, 3)
+
+        //when
+        val sum = listOfNumbers.reduce { a, b -> a + b }
+
+        //then
+        assertEquals(6, sum)
+    }
+}
\ No newline at end of file