diff --git a/guest/core-java/pom.xml b/guest/core-java/pom.xml
index c3042ca94aaa..b3c6ba956433 100644
--- a/guest/core-java/pom.xml
+++ b/guest/core-java/pom.xml
@@ -41,11 +41,18 @@
             <version>${org.hamcrest.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <properties>
         <log4j2.version>2.8.2</log4j2.version>
         <org.hamcrest.version>1.3</org.hamcrest.version>
+        <assertj.version>3.6.1</assertj.version>
     </properties>
 
 </project>
\ No newline at end of file
diff --git a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitamin.java b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitamin.java
similarity index 91%
rename from core-java/src/main/java/com/baeldung/optionalparams/MultiVitamin.java
rename to guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitamin.java
index 709e74eac075..90cb49b32142 100644
--- a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitamin.java
+++ b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitamin.java
@@ -1,50 +1,50 @@
-package com.baeldung.optionalparams;
-
-public class MultiVitamin {
-
-    private String name;    // required
-    private int vitaminA;   // in mcg
-    private int vitaminC;   // in mg
-    private int calcium;    // in mg
-    private int iron;       // in mg
-
-    public MultiVitamin(String name) {
-        this.name = name;
-    }
-
-    public String getName() {
-        return name;
-    }
-
-    public int getVitaminA() {
-        return vitaminA;
-    }
-
-    public void setVitaminA(int vitaminA) {
-        this.vitaminA = vitaminA;
-    }
-
-    public int getVitaminC() {
-        return vitaminC;
-    }
-
-    public void setVitaminC(int vitaminC) {
-        this.vitaminC = vitaminC;
-    }
-
-    public int getCalcium() {
-        return calcium;
-    }
-
-    public void setCalcium(int calcium) {
-        this.calcium = calcium;
-    }
-
-    public int getIron() {
-        return iron;
-    }
-
-    public void setIron(int iron) {
-        this.iron = iron;
-    }
+package com.stackify.optionalparams;
+
+public class MultiVitamin {
+
+    private String name;    // required
+    private int vitaminA;   // in mcg
+    private int vitaminC;   // in mg
+    private int calcium;    // in mg
+    private int iron;       // in mg
+
+    public MultiVitamin(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getVitaminA() {
+        return vitaminA;
+    }
+
+    public void setVitaminA(int vitaminA) {
+        this.vitaminA = vitaminA;
+    }
+
+    public int getVitaminC() {
+        return vitaminC;
+    }
+
+    public void setVitaminC(int vitaminC) {
+        this.vitaminC = vitaminC;
+    }
+
+    public int getCalcium() {
+        return calcium;
+    }
+
+    public void setCalcium(int calcium) {
+        this.calcium = calcium;
+    }
+
+    public int getIron() {
+        return iron;
+    }
+
+    public void setIron(int iron) {
+        this.iron = iron;
+    }
 }
\ No newline at end of file
diff --git a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminAllowingNulls.java b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminAllowingNulls.java
similarity index 95%
rename from core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminAllowingNulls.java
rename to guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminAllowingNulls.java
index 36d178783a8a..1d2a61354d88 100644
--- a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminAllowingNulls.java
+++ b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminAllowingNulls.java
@@ -1,4 +1,4 @@
-package com.baeldung.optionalparams;
+package com.stackify.optionalparams;
 
 public class MultiVitaminAllowingNulls {
 
diff --git a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminOverloading.java b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminOverloading.java
similarity index 93%
rename from core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminOverloading.java
rename to guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminOverloading.java
index e1d3032fd3c2..e9dcb2509b85 100644
--- a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminOverloading.java
+++ b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminOverloading.java
@@ -1,56 +1,56 @@
-package com.baeldung.optionalparams;
-
-public class MultiVitaminOverloading {
-
-    static final int DEFAULT_IRON_AMOUNT = 20;
-
-    private final String name;    // required
-    private final int vitaminA;   // in mcg
-    private final int vitaminC;   // in mg
-    private final int calcium;    // in mg
-    private final int iron;       // in mg
-
-    public MultiVitaminOverloading(String name) {
-        this(name, 0);
-    }
-
-    public MultiVitaminOverloading(String name, int vitaminA) {
-        this(name, vitaminA, 0);
-    }
-
-    public MultiVitaminOverloading(String name, int vitaminA, int vitaminC) {
-        this(name, vitaminA, vitaminC, 0);
-    }
-
-    public MultiVitaminOverloading(String name, int vitaminA, int vitaminC, int calcium) {
-        this(name, vitaminA, vitaminC, calcium, DEFAULT_IRON_AMOUNT);
-    }
-
-    public MultiVitaminOverloading(String name, int vitaminA, int vitaminC, int calcium, int iron) {
-        this.name = name;
-        this.vitaminA = vitaminA;
-        this.vitaminC = vitaminC;
-        this.calcium = calcium;
-        this.iron = iron;
-    }
-
-    public String getName() {
-        return name;
-    }
-
-    public int getVitaminA() {
-        return vitaminA;
-    }
-
-    public int getVitaminC() {
-        return vitaminC;
-    }
-
-    public int getCalcium() {
-        return calcium;
-    }
-
-    public int getIron() {
-        return iron;
-    }
+package com.stackify.optionalparams;
+
+public class MultiVitaminOverloading {
+
+    static final int DEFAULT_IRON_AMOUNT = 20;
+
+    private final String name;    // required
+    private final int vitaminA;   // in mcg
+    private final int vitaminC;   // in mg
+    private final int calcium;    // in mg
+    private final int iron;       // in mg
+
+    public MultiVitaminOverloading(String name) {
+        this(name, 0);
+    }
+
+    public MultiVitaminOverloading(String name, int vitaminA) {
+        this(name, vitaminA, 0);
+    }
+
+    public MultiVitaminOverloading(String name, int vitaminA, int vitaminC) {
+        this(name, vitaminA, vitaminC, 0);
+    }
+
+    public MultiVitaminOverloading(String name, int vitaminA, int vitaminC, int calcium) {
+        this(name, vitaminA, vitaminC, calcium, DEFAULT_IRON_AMOUNT);
+    }
+
+    public MultiVitaminOverloading(String name, int vitaminA, int vitaminC, int calcium, int iron) {
+        this.name = name;
+        this.vitaminA = vitaminA;
+        this.vitaminC = vitaminC;
+        this.calcium = calcium;
+        this.iron = iron;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getVitaminA() {
+        return vitaminA;
+    }
+
+    public int getVitaminC() {
+        return vitaminC;
+    }
+
+    public int getCalcium() {
+        return calcium;
+    }
+
+    public int getIron() {
+        return iron;
+    }
 }
\ No newline at end of file
diff --git a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminStaticFactoryMethods.java b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminStaticFactoryMethods.java
similarity index 97%
rename from core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminStaticFactoryMethods.java
rename to guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminStaticFactoryMethods.java
index ca7ab0f6cf19..229a2f000425 100644
--- a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminStaticFactoryMethods.java
+++ b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminStaticFactoryMethods.java
@@ -1,4 +1,4 @@
-package com.baeldung.optionalparams;
+package com.stackify.optionalparams;
 
 public class MultiVitaminStaticFactoryMethods {
 
diff --git a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminWithBuilder.java b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminWithBuilder.java
similarity index 94%
rename from core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminWithBuilder.java
rename to guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminWithBuilder.java
index e1b2920e9ae9..8097074b8697 100644
--- a/core-java/src/main/java/com/baeldung/optionalparams/MultiVitaminWithBuilder.java
+++ b/guest/core-java/src/main/java/com/stackify/optionalparams/MultiVitaminWithBuilder.java
@@ -1,77 +1,77 @@
-package com.baeldung.optionalparams;
-
-public class MultiVitaminWithBuilder {
-
-    private final String name;    // required
-    private final int vitaminA;   // in mcg
-    private final int vitaminC;   // in mg
-    private final int calcium;    // in mg
-    private final int iron;       // in mg
-
-    private MultiVitaminWithBuilder(MultiVitaminBuilder builder) {
-        this.name = builder.name;
-        this.vitaminA = builder.vitaminA;
-        this.vitaminC = builder.vitaminC;
-        this.calcium = builder.calcium;
-        this.iron = builder.iron;
-    }
-
-    public String getName() {
-        return name;
-    }
-
-    public int getVitaminA() {
-        return vitaminA;
-    }
-
-    public int getVitaminC() {
-        return vitaminC;
-    }
-
-    public int getCalcium() {
-        return calcium;
-    }
-
-    public int getIron() {
-        return iron;
-    }
-
-    public static class MultiVitaminBuilder {
-
-        private static final int ZERO = 0;
-
-        private final String name; // required
-        private int vitaminA = ZERO;
-        private int vitaminC = ZERO;
-        private int calcium = ZERO;
-        private int iron = ZERO;
-
-        public MultiVitaminBuilder(String name) {
-            this.name = name;
-        }
-
-        public MultiVitaminBuilder withVitaminA(int vitaminA) {
-            this.vitaminA = vitaminA;
-            return this;
-        }
-
-        public MultiVitaminBuilder withVitaminC(int vitaminC) {
-            this.vitaminC = vitaminC;
-            return this;
-        }
-
-        public MultiVitaminBuilder withCalcium(int calcium) {
-            this.calcium = calcium;
-            return this;
-        }
-
-        public MultiVitaminBuilder withIron(int iron) {
-            this.iron = iron;
-            return this;
-        }
-
-        public MultiVitaminWithBuilder build() {
-            return new MultiVitaminWithBuilder(this);
-        }
-    }
-}
+package com.stackify.optionalparams;
+
+public class MultiVitaminWithBuilder {
+
+    private final String name;    // required
+    private final int vitaminA;   // in mcg
+    private final int vitaminC;   // in mg
+    private final int calcium;    // in mg
+    private final int iron;       // in mg
+
+    private MultiVitaminWithBuilder(MultiVitaminBuilder builder) {
+        this.name = builder.name;
+        this.vitaminA = builder.vitaminA;
+        this.vitaminC = builder.vitaminC;
+        this.calcium = builder.calcium;
+        this.iron = builder.iron;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getVitaminA() {
+        return vitaminA;
+    }
+
+    public int getVitaminC() {
+        return vitaminC;
+    }
+
+    public int getCalcium() {
+        return calcium;
+    }
+
+    public int getIron() {
+        return iron;
+    }
+
+    public static class MultiVitaminBuilder {
+
+        private static final int ZERO = 0;
+
+        private final String name; // required
+        private int vitaminA = ZERO;
+        private int vitaminC = ZERO;
+        private int calcium = ZERO;
+        private int iron = ZERO;
+
+        public MultiVitaminBuilder(String name) {
+            this.name = name;
+        }
+
+        public MultiVitaminBuilder withVitaminA(int vitaminA) {
+            this.vitaminA = vitaminA;
+            return this;
+        }
+
+        public MultiVitaminBuilder withVitaminC(int vitaminC) {
+            this.vitaminC = vitaminC;
+            return this;
+        }
+
+        public MultiVitaminBuilder withCalcium(int calcium) {
+            this.calcium = calcium;
+            return this;
+        }
+
+        public MultiVitaminBuilder withIron(int iron) {
+            this.iron = iron;
+            return this;
+        }
+
+        public MultiVitaminWithBuilder build() {
+            return new MultiVitaminWithBuilder(this);
+        }
+    }
+}
diff --git a/core-java/src/test/java/com/baeldung/optionalparams/OptionalParamsUnitTest.java b/guest/core-java/src/test/java/com/stackify/optionalparams/OptionalParamsUnitTest.java
similarity index 99%
rename from core-java/src/test/java/com/baeldung/optionalparams/OptionalParamsUnitTest.java
rename to guest/core-java/src/test/java/com/stackify/optionalparams/OptionalParamsUnitTest.java
index 4f3c31822b46..947ce83a9025 100644
--- a/core-java/src/test/java/com/baeldung/optionalparams/OptionalParamsUnitTest.java
+++ b/guest/core-java/src/test/java/com/stackify/optionalparams/OptionalParamsUnitTest.java
@@ -1,4 +1,4 @@
-package com.baeldung.optionalparams;
+package com.stackify.optionalparams;
 
 import static org.assertj.core.api.Assertions.assertThat;