diff --git a/Dockerfile b/Dockerfile
index f1e2e90..ca7f76f 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,8 +1,8 @@
-FROM eclipse-temurin:17-jdk AS builder-base
+FROM eclipse-temurin:21-jdk AS builder-base
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
-      dos2unix \
       binutils \
+      dos2unix \
       fakeroot \
       rpm && \
     rm -rf /var/lib/apt/lists/*
diff --git a/src/test/java/com/github/mfl28/boundingboxeditor/BoundingBoxEditorTestBase.java b/src/test/java/com/github/mfl28/boundingboxeditor/BoundingBoxEditorTestBase.java
index ce875cb..be49459 100644
--- a/src/test/java/com/github/mfl28/boundingboxeditor/BoundingBoxEditorTestBase.java
+++ b/src/test/java/com/github/mfl28/boundingboxeditor/BoundingBoxEditorTestBase.java
@@ -113,8 +113,8 @@ protected static Stage getTopModalStage(FxRobot robot, String title) {
         // It is needed to get the first found modal window.
         return robot.listWindows()
                 .stream()
-                .filter(window -> window instanceof Stage)
-                .map(window -> (Stage) window)
+                .filter(Stage.class::isInstance)
+                .map(Stage.class::cast)
                 .filter(stage -> stage.getModality() == Modality.APPLICATION_MODAL)
                 .filter(stage -> stage.getTitle().equals(title))
                 .findFirst()
@@ -247,7 +247,7 @@ protected void onStart(Stage stage) {
     }
 
     @AfterEach
-    protected void tearDown() throws TimeoutException {
+    void tearDown() throws TimeoutException {
         FxToolkit.cleanupStages();
         FxToolkit.hideStage();
         // Make sure FileChangeWatcher is interrupted.
@@ -554,8 +554,8 @@ private <T extends Node> boolean nodePresentAndVisibleAs(FxRobot robot, String i
     private boolean isTopModalStagePresent(FxRobot robot) {
         return robot.listWindows()
                 .stream()
-                .filter(window -> window instanceof Stage)
-                .map(window -> (Stage) window)
+                .filter(Stage.class::isInstance)
+                .map(Stage.class::cast)
                 .anyMatch(stage -> stage.getModality() == Modality.APPLICATION_MODAL);
     }
 
diff --git a/src/test/java/com/github/mfl28/boundingboxeditor/controller/ControllerTests.java b/src/test/java/com/github/mfl28/boundingboxeditor/controller/ControllerTests.java
index 1a1f964..8761d84 100644
--- a/src/test/java/com/github/mfl28/boundingboxeditor/controller/ControllerTests.java
+++ b/src/test/java/com/github/mfl28/boundingboxeditor/controller/ControllerTests.java
@@ -129,11 +129,11 @@ void onExportAnnotation_PVOC_WhenPreviouslyImportedAnnotation_ShouldProduceEquiv
                                 .isHasAssignedBoundingShapes()
                                 && mainView.getCurrentBoundingShapes()
                                 .stream()
-                                .filter(viewable -> viewable instanceof BoundingBoxView)
+                                .filter(BoundingBoxView.class::isInstance)
                                 .count() == 8
                                 && mainView.getCurrentBoundingShapes()
                                 .stream()
-                                .filter(viewable -> viewable instanceof BoundingPolygonView)
+                                .filter(BoundingPolygonView.class::isInstance)
                                 .count() == 1),
                 () -> saveScreenshotAndReturnMessage(testinfo,
                         "Bounding shape counts did not match " +
@@ -273,11 +273,11 @@ void onExportAnnotation_YOLO_WhenPreviouslyImportedAnnotation_ShouldProduceEquiv
                                 .isHasAssignedBoundingShapes()
                                 && mainView.getCurrentBoundingShapes()
                                 .stream()
-                                .filter(viewable -> viewable instanceof BoundingBoxView)
+                                .filter(BoundingBoxView.class::isInstance)
                                 .count() == 9
                                 && mainView.getCurrentBoundingShapes()
                                 .stream()
-                                .filter(viewable -> viewable instanceof BoundingPolygonView)
+                                .filter(BoundingPolygonView.class::isInstance)
                                 .count() == 1),
                 () -> saveScreenshotAndReturnMessage(testinfo,
                         "Bounding shape counts did not match " +
@@ -407,11 +407,11 @@ void onExportAnnotation_JSON_WhenPreviouslyImportedAnnotation_ShouldProduceEquiv
                                 .isHasAssignedBoundingShapes()
                                 && mainView.getCurrentBoundingShapes()
                                 .stream()
-                                .filter(viewable -> viewable instanceof BoundingBoxView)
+                                .filter(BoundingBoxView.class::isInstance)
                                 .count() == 8
                                 && mainView.getCurrentBoundingShapes()
                                 .stream()
-                                .filter(viewable -> viewable instanceof BoundingPolygonView)
+                                .filter(BoundingPolygonView.class::isInstance)
                                 .count() == 1),
                 () -> saveScreenshotAndReturnMessage(testinfo,
                         "Bounding shape counts did not match " +
@@ -1227,10 +1227,10 @@ void onExportAnnotation_CSV_WhenPreviouslyImportedAnnotation_ShouldProduceEquiva
                                 .isHasAssignedBoundingShapes()
                                 && mainView.getCurrentBoundingShapes()
                                 .stream()
-                                .filter(viewable -> viewable instanceof BoundingBoxView)
+                                .filter(BoundingBoxView.class::isInstance)
                                 .count() == 3
                                 && mainView.getCurrentBoundingShapes()
-                                .stream().noneMatch(viewable -> viewable instanceof BoundingPolygonView)),
+                                .stream().noneMatch(BoundingPolygonView.class::isInstance)),
                 () -> saveScreenshotAndReturnMessage(testinfo,
                         "Bounding shape counts did not match " +
                                 "within " + TIMEOUT_DURATION_IN_SEC +