refactor some classes

jadx-gui/src/main/java/jadx/gui/MainWindow.java

@@ -81,10 +81,12 @@ public class MainWindow extends JFrame {
 	private final JadxWrapper wrapper;
 
 	private JPanel mainPanel;
+
 	private JTree tree;
-	private final JTabbedPane tabbedPane = new JTabbedPane();
 	private DefaultTreeModel treeModel;
-	private Map<JClass, Component> openTabs = new HashMap<JClass, Component>();
+
+	private final JTabbedPane tabbedPane = new JTabbedPane();
+	private final Map<JClass, Component> openTabs = new HashMap<JClass, Component>();
 
 	public MainWindow(JadxWrapper wrapper) {
 		this.wrapper = wrapper;

jadx-gui/src/main/java/jadx/gui/treemodel/JClass.java

@@ -50,7 +50,7 @@ public class JClass extends JNode {
 	}
 
 	@Override
-	public void updateChilds() {
+	public synchronized void updateChilds() {
 		removeAllChildren();
 		if (!loaded) {
 			add(new TextNode(NLS.str("tree.loading")));

jadx-gui/src/main/java/jadx/gui/treemodel/JPackage.java

@@ -15,8 +15,8 @@ public class JPackage extends JNode implements Comparable<JPackage> {
 	private static final ImageIcon PACKAGE_ICON = Utils.openIcon("package_obj");
 
 	private String name;
-	private List<JClass> classes;
-	private List<JPackage> innerPackages = new ArrayList<JPackage>(1);
+	private final List<JClass> classes;
+	private final List<JPackage> innerPackages = new ArrayList<JPackage>(1);
 
 	public JPackage(JavaPackage pkg) {
 		this.name = pkg.getName();