diff --git a/src/main/java/de/neemann/digital/gui/Settings.java b/src/main/java/de/neemann/digital/gui/Settings.java
index 6c7084edd..cee2b1480 100644
--- a/src/main/java/de/neemann/digital/gui/Settings.java
+++ b/src/main/java/de/neemann/digital/gui/Settings.java
@@ -10,21 +10,26 @@ import de.neemann.digital.draw.elements.Circuit;
 
 import java.io.*;
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 /**
  * The Settings of Digital
- * <p/>
+ * <p>
  * Created by Helmut.Neemann on 11.05.2016.
  */
 public final class Settings implements AttributeListener {
 
+    private static final List<Key> INT_LIST = new ArrayList<>();
+
     /**
      * The list of supported attributes.
      */
-    public static final ArrayList<Key> SETTINGS_KEYS = new ArrayList<>();
+    public static final List<Key> SETTINGS_KEYS = Collections.unmodifiableList(INT_LIST);
+
 
     static {
-        SETTINGS_KEYS.add(Keys.SETTINGS_IEEE_SHAPES);
+        INT_LIST.add(Keys.SETTINGS_IEEE_SHAPES);
     }
 
     private static final class SettingsHolder {
diff --git a/src/main/java/de/neemann/digital/gui/components/AttributeDialog.java b/src/main/java/de/neemann/digital/gui/components/AttributeDialog.java
index 97126e5c9..ee3a95275 100644
--- a/src/main/java/de/neemann/digital/gui/components/AttributeDialog.java
+++ b/src/main/java/de/neemann/digital/gui/components/AttributeDialog.java
@@ -15,7 +15,7 @@ import java.util.ArrayList;
  */
 public class AttributeDialog extends JDialog {
 
-    private final ArrayList<EditorHolder> editors;
+    private final java.util.List<EditorHolder> editors;
     private boolean changed = false;
 
     /**
@@ -25,7 +25,7 @@ public class AttributeDialog extends JDialog {
      * @param list              the list of keys which are to edit
      * @param elementAttributes the data stored
      */
-    public AttributeDialog(Component parent, ArrayList<Key> list, ElementAttributes elementAttributes) {
+    public AttributeDialog(Component parent, java.util.List<Key> list, ElementAttributes elementAttributes) {
         this(parent, null, list, elementAttributes);
     }
 
@@ -37,7 +37,7 @@ public class AttributeDialog extends JDialog {
      * @param list              the list of keys which are to edit
      * @param elementAttributes the data stored
      */
-    public AttributeDialog(Component parent, Point pos, ArrayList<Key> list, ElementAttributes elementAttributes) {
+    public AttributeDialog(Component parent, Point pos, java.util.List<Key> list, ElementAttributes elementAttributes) {
         super(SwingUtilities.getWindowAncestor(parent), Lang.get("attr_dialogTitle"), ModalityType.APPLICATION_MODAL);
         setDefaultCloseOperation(DISPOSE_ON_CLOSE);