This PR is related to BAEL-6315 (#15337)

* This commit is related to BAEL-6315

This commit aims to add two classes Contact and Person.

* This commit is related to BAEL-6315

This commit aims to add a test class DeserializationUnitTest.

core-java-modules/core-java-20/src/main/java/com/baeldung/deserialization/Contact.java

@@ -0,0 +1,5 @@
+package com.baeldung.deserialization;
+
+public record Contact(String email, String phone) {
+    // Constructor, getters, and other methods are automatically generated
+}

core-java-modules/core-java-20/src/main/java/com/baeldung/deserialization/Person.java

@@ -0,0 +1,5 @@
+package com.baeldung.deserialization;
+
+public record Person(String name, int age, String address, Contact contact) {
+    // Constructor, getters, and other methods are automatically generated
+}

core-java-modules/core-java-20/src/test/java/com/baeldung/deserialization/DeserializationUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.deserialization;
+
+import com.google.gson.Gson;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+public class DeserializationUnitTest {
+
+    @Test
+    public void givenJsonString_whenDeserialized_thenPersonRecordCreated() {
+        String json = "{\"name\":\"John Doe\",\"age\":30,\"address\":\"123 Main St\"}";
+
+        Person person = new Gson().fromJson(json, Person.class);
+
+        assertEquals("John Doe", person.name());
+        assertEquals(30, person.age());
+        assertEquals("123 Main St", person.address());
+    }
+
+    @Test
+    public void givenNestedJsonString_whenDeserialized_thenPersonRecordCreated() {
+        String json = "{\"name\":\"John Doe\",\"age\":30,\"address\":\"123 Main St\",\"contact\":{\"email\":\"john.doe@example.com\",\"phone\":\"555-1234\"}}";
+
+        Person person = new Gson().fromJson(json, Person.class);
+
+        assertNotNull(person);
+        assertEquals("John Doe", person.name());
+        assertEquals(30, person.age());
+        assertEquals("123 Main St", person.address());
+
+        Contact contact = person.contact();
+
+        assertNotNull(contact);
+        assertEquals("john.doe@example.com", contact.email());
+        assertEquals("555-1234", contact.phone());
+    }
+}