diff --git a/core-kotlin/src/test/kotlin/com/baeldung/random/RandomStringTest.kt b/core-kotlin/src/test/kotlin/com/baeldung/random/RandomStringTest.kt
index a2a1ac58e3..3c7bc44ea8 100644
--- a/core-kotlin/src/test/kotlin/com/baeldung/random/RandomStringTest.kt
+++ b/core-kotlin/src/test/kotlin/com/baeldung/random/RandomStringTest.kt
@@ -13,14 +13,7 @@ const val STRING_LENGTH = 10
 const val ALPHANUMERIC_REGEX = "[a-zA-Z0-9]+"
 
 class RandomStringTest {
-
-    private val charPool = ArrayList<Char>()
-
-    init {
-        charPool.addAll('a'..'z')
-        charPool.addAll('A'..'Z')
-        charPool.addAll('0'..'9')
-    }
+    private val charPool : List<Char> = ('a'..'z') + ('A'..'Z') + ('0'..'9')
 
     @Test
     fun givenAStringLength_whenUsingJava_thenReturnAlphanumericString() {