diff --git a/core-java-modules/core-java-collections-7/src/main/java/com/baeldung/entitycollection/IdExtractor.java b/core-java-modules/core-java-collections-7/src/main/java/com/baeldung/entitycollection/IdExtractor.java
new file mode 100644
index 000000000000..2503b1b8d387
--- /dev/null
+++ b/core-java-modules/core-java-collections-7/src/main/java/com/baeldung/entitycollection/IdExtractor.java
@@ -0,0 +1,27 @@
+package com.baeldung.entitycollection;
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+public class IdExtractor {
+
+    public static List<Long> extractIdsClassic(List<User> users) {
+        List<Long> ids = new ArrayList<>();
+        for (User user : users) {
+            ids.add(user.getId());
+        }
+        return ids;
+    }
+
+    public static List<Long> extractIdsStream(List<User> users) {
+        return users.stream()
+                .map(User::getId)
+                .collect(Collectors.toList());
+    }
+
+    public static Set<Long> extractUniqueIds(List<User> users) {
+        return users.stream()
+                .map(User::getId)
+                .collect(Collectors.toSet());
+    }
+}
diff --git a/core-java-modules/core-java-collections-7/src/main/java/com/baeldung/entitycollection/User.java b/core-java-modules/core-java-collections-7/src/main/java/com/baeldung/entitycollection/User.java
new file mode 100644
index 000000000000..f5a0bb0e2e68
--- /dev/null
+++ b/core-java-modules/core-java-collections-7/src/main/java/com/baeldung/entitycollection/User.java
@@ -0,0 +1,15 @@
+package com.baeldung.entitycollection;
+
+public class User {
+    private final Long id;
+    private final String name;
+
+    public User(Long id, String name) {
+        this.id = id;
+        this.name = name;
+    }
+
+    public Long getId() {
+        return id;
+    }
+}
diff --git a/core-java-modules/core-java-collections-7/src/test/java/com/baeldung/entitycollection/IdExtractionUnitTest.java b/core-java-modules/core-java-collections-7/src/test/java/com/baeldung/entitycollection/IdExtractionUnitTest.java
new file mode 100644
index 000000000000..34187a9e9b74
--- /dev/null
+++ b/core-java-modules/core-java-collections-7/src/test/java/com/baeldung/entitycollection/IdExtractionUnitTest.java
@@ -0,0 +1,79 @@
+package com.baeldung.entitycollection;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.*;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class IdExtractionUnitTest {
+
+    @Test
+    void givenListOfUsers_whenUsingClassicLoop_thenReturnListOfIds() {
+        List<User> users = Arrays.asList(
+                new User(1L, "A"),
+                new User(2L, "B"),
+                new User(3L, "C")
+        );
+
+        List<Long> ids = IdExtractor.extractIdsClassic(users);
+
+        assertEquals(Arrays.asList(1L, 2L, 3L), ids);
+    }
+
+    @Test
+    void givenEmptyUsersList_whenUsingClassicLoop_thenReturnEmptyList() {
+        List<User> users = List.of();
+        List<Long> ids = IdExtractor.extractIdsClassic(users);
+        assertTrue(ids.isEmpty());
+    }
+
+    @Test
+    void givenUsersList_whenUsingStream_thenReturnListOfIds() {
+        List<User> users = Arrays.asList(
+                new User(10L, "A"),
+                new User(20L, "B")
+        );
+
+        List<Long> ids = IdExtractor.extractIdsStream(users);
+        assertEquals(Arrays.asList(10L, 20L), ids);
+    }
+
+    @Test
+    void givenEmptyUsersList_whenUsingStream_thenReturnEmptyList() {
+        List<User> users = List.of();
+        List<Long> ids = IdExtractor.extractIdsStream(users);
+        assertTrue(ids.isEmpty());
+    }
+
+    @Test
+    void givenUsersWithNullIds_whenUsingStream_thenAllowNullValuesInList() {
+        List<User> users = Arrays.asList(
+                new User(null, "A"),
+                new User(5L, "B")
+        );
+
+        List<Long> ids = IdExtractor.extractIdsStream(users);
+        assertEquals(Arrays.asList(null, 5L), ids);
+    }
+
+    @Test
+    void givenUsersWithDuplicateIds_whenUsingUniqueIdExtractor_thenReturnUniqueSet() {
+        List<User> users = Arrays.asList(
+                new User(1L, "A"),
+                new User(1L, "B"),
+                new User(2L, "C")
+        );
+
+        Set<Long> ids = IdExtractor.extractUniqueIds(users);
+        assertEquals(Set.of(1L, 2L), ids);
+    }
+
+    @Test
+    void givenEmptyUsersList_whenUsingUniqueIdExtractor_thenReturnEmptySet() {
+        List<User> users = List.of();
+        Set<Long> ids = IdExtractor.extractUniqueIds(users);
+        assertTrue(ids.isEmpty());
+    }
+}
+
diff --git a/json-modules/json-arrays/src/test/java/com/baeldung/jsonarray/JsonArrayToIntArrayUnitTest.java b/json-modules/json-arrays/src/test/java/com/baeldung/jsonarray/JsonArrayToIntArrayUnitTest.java
new file mode 100644
index 000000000000..3c5a68abd22d
--- /dev/null
+++ b/json-modules/json-arrays/src/test/java/com/baeldung/jsonarray/JsonArrayToIntArrayUnitTest.java
@@ -0,0 +1,58 @@
+package com.baeldung.jsonarray;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.json.JSONArray;
+import org.junit.jupiter.api.Test;
+
+import java.util.stream.IntStream;
+
+
+class JsonArrayToIntArrayUnitTest {
+
+    @Test
+    void givenJsonArray_whenUsingLoop_thenIntArrayIsReturned() {
+        JSONArray jsonArray = new JSONArray("[1, 2, 3]");
+        int[] result = new int[jsonArray.length()];
+        for (int i = 0; i < jsonArray.length(); i++) {
+            result[i] = jsonArray.getInt(i);
+        }
+
+        assertArrayEquals(new int[]{1, 2, 3}, result);
+    }
+
+    @Test
+    void givenJsonArray_whenUsingStreams_thenIntArrayIsReturned() {
+        JSONArray jsonArray = new JSONArray("[10, 20, 30]");
+        int[] result = IntStream.range(0, jsonArray.length())
+                .map(jsonArray::getInt)
+                .toArray();
+
+        assertArrayEquals(new int[]{10, 20, 30}, result);
+    }
+
+    @Test
+    void givenNullJsonArray_whenConvertingSafely_thenEmptyArrayIsReturned() {
+        int[] result = toIntArraySafely(null);
+        assertEquals(0, result.length);
+    }
+
+    @Test
+    void givenEmptyJsonArray_whenConvertingSafely_thenEmptyArrayIsReturned() {
+        JSONArray jsonArray = new JSONArray();
+        int[] result = toIntArraySafely(jsonArray);
+        assertEquals(0, result.length);
+    }
+
+    private int[] toIntArraySafely(JSONArray jsonArray) {
+        if (jsonArray == null || jsonArray.isEmpty()) {
+            return new int[0];
+        }
+
+        int[] result = new int[jsonArray.length()];
+        for (int i = 0; i < jsonArray.length(); i++) {
+            result[i] = jsonArray.getInt(i);
+        }
+        return result;
+    }
+}