✨ BAEL-3237 AutoValue Builder with defensive copies

Author: gilday

code-generation/src/main/java/com/baeldung/autovalue/Person.java

@@ -0,0 +1,38 @@
+package com.baeldung.autovalue;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import com.google.auto.value.AutoValue;
+
+@AutoValue
+public abstract class Person {
+
+    public abstract String name();
+
+    public abstract List<String> favoriteMovies();
+
+    public static Builder builder() {
+        return new AutoValue_Person.Builder();
+    }
+
+    @AutoValue.Builder
+    public static abstract class Builder {
+
+        public abstract Builder name(String value);
+
+        public abstract Builder favoriteMovies(List<String> value);
+
+        abstract List<String> favoriteMovies();
+
+        abstract Person autoBuild();
+
+        public Person build() {
+            List<String> favoriteMovies = favoriteMovies();
+            List<String> copy = Collections.unmodifiableList(new ArrayList<>(favoriteMovies));
+            favoriteMovies(copy);
+            return autoBuild();
+        }
+    }
+}

code-generation/src/test/java/com/baeldung/autovalue/PersonUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.autovalue;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Test;
+
+/**
+ * Unit Test which verifies that the {@link Person} value object creates defensive copies of its favoriteMovies list.
+ */
+public class PersonUnitTest {
+
+    @Test
+    public void givenNewPerson_whenModifyOriginalList_thenValueObjectIsNotAlsoModified() {
+        // GIVEN new Person
+        List<String> originalFavoriteMoviesList = new ArrayList<String>();
+        originalFavoriteMoviesList.add("Training Day");
+        originalFavoriteMoviesList.add("Fast and the Furious");
+        Person person = Person.builder()
+            .name("Dan")
+            .favoriteMovies(originalFavoriteMoviesList)
+            .build();
+
+        // WHEN modify original list
+        originalFavoriteMoviesList.add("Friday");
+
+        // THEN Person remains unaffected
+        assertFalse(person.favoriteMovies()
+            .contains("Friday"));
+        assertEquals(2, person.favoriteMovies()
+            .size());
+    }
+
+}