diff --git a/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/Person.java b/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/Person.java
new file mode 100644
index 00000000..39f47e51
--- /dev/null
+++ b/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/Person.java
@@ -0,0 +1,23 @@
+package com.example.refactoring._06_mutable_data._23_change_reference_to_value;
+
+public class Person {
+
+    private TelephoneNumber officeTelephoneNumber;
+
+    public String officeAreaCode() {
+        return this.officeTelephoneNumber.areaCode();
+    }
+
+    public void officeAreaCode(String areaCode) {
+        this.officeTelephoneNumber = new TelephoneNumber(areaCode, this.officeNumber());
+    }
+
+    public String officeNumber() {
+        return this.officeTelephoneNumber.number();
+    }
+
+    public void officeNumber(String number) {
+        this.officeTelephoneNumber = new TelephoneNumber(this.officeAreaCode(), number);
+    }
+
+}
diff --git a/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/TelephoneNumber.java b/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/TelephoneNumber.java
new file mode 100644
index 00000000..e6ed3f71
--- /dev/null
+++ b/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/TelephoneNumber.java
@@ -0,0 +1,36 @@
+package com.example.refactoring._06_mutable_data._23_change_reference_to_value;
+
+import java.util.Objects;
+
+public class TelephoneNumber {
+
+    private final String areaCode;
+
+    private final String number;
+
+    public TelephoneNumber(String areaCode, String number) {
+        this.areaCode = areaCode;
+        this.number = number;
+    }
+
+    public String areaCode() {
+        return areaCode;
+    }
+
+    public String number() {
+        return number;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(areaCode, number);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null || getClass() != obj.getClass()) return false;
+        TelephoneNumber that = (TelephoneNumber) obj;
+        return Objects.equals(areaCode, that.areaCode) && Objects.equals(number, that.number);
+    }
+}
diff --git a/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/before/Person.java b/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/before/Person.java
new file mode 100644
index 00000000..3827b658
--- /dev/null
+++ b/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/before/Person.java
@@ -0,0 +1,23 @@
+package com.example.refactoring._06_mutable_data._23_change_reference_to_value.before;
+
+public class Person {
+
+    private TelephoneNumber officeTelephoneNumber;
+
+    public String officeAreaCode() {
+        return this.officeTelephoneNumber.areaCode();
+    }
+
+    public void officeAreaCode(String areaCode) {
+        this.officeTelephoneNumber.areaCode(areaCode);
+    }
+
+    public String officeNumber() {
+        return this.officeTelephoneNumber.number();
+    }
+
+    public void officeNumber(String number) {
+        this.officeTelephoneNumber.number(number);
+    }
+
+}
diff --git a/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/before/TelephoneNumber.java b/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/before/TelephoneNumber.java
new file mode 100644
index 00000000..389738ee
--- /dev/null
+++ b/refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/before/TelephoneNumber.java
@@ -0,0 +1,24 @@
+package com.example.refactoring._06_mutable_data._23_change_reference_to_value.before;
+
+public class TelephoneNumber {
+
+    private String areaCode;
+
+    private String number;
+
+    public String areaCode() {
+        return areaCode;
+    }
+
+    public void areaCode(String areaCode) {
+        this.areaCode = areaCode;
+    }
+
+    public String number() {
+        return number;
+    }
+
+    public void number(String number) {
+        this.number = number;
+    }
+}
diff --git a/refactoring/src/test/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/TelephoneNumberTest.java b/refactoring/src/test/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/TelephoneNumberTest.java
new file mode 100644
index 00000000..78de2010
--- /dev/null
+++ b/refactoring/src/test/java/com/example/refactoring/_06_mutable_data/_23_change_reference_to_value/TelephoneNumberTest.java
@@ -0,0 +1,17 @@
+package com.example.refactoring._06_mutable_data._23_change_reference_to_value;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class TelephoneNumberTest {
+
+    @Test
+    void testEquals() {
+        TelephoneNumber telephoneNumber1 = new TelephoneNumber("123", "1234");
+        TelephoneNumber telephoneNumber2 = new TelephoneNumber("123", "1234");
+
+        assertEquals(telephoneNumber1, telephoneNumber2);
+    }
+
+}
\ No newline at end of file