refactor: Controller使用sigleton，避免多次创建对象

src/main/java/org/jcnc/jnotepad/LunchApp.java

@@ -23,7 +23,7 @@ public class LunchApp extends Application {
     private static final ExecutorService threadPool = Executors.newCachedThreadPool();
     public static boolean isRelevance = true;
 
-    Controller controller = new Controller();
+    Controller controller = Controller.getInstance();
 
     View view;
 

src/main/java/org/jcnc/jnotepad/controller/event/handler/NewFile.java

@@ -23,7 +23,7 @@ public class NewFile implements EventHandler<ActionEvent> {
     @Override
     public void handle(ActionEvent event) {
         // 获取控制器
-        Controller controller = new Controller();
+        Controller controller = Controller.getInstance();
 
         // 创建一个新的文本编辑区
         TextArea textArea = new TextArea();

src/main/java/org/jcnc/jnotepad/controller/event/handler/OpenFile.java

@@ -25,7 +25,7 @@ public class OpenFile implements EventHandler<ActionEvent> {
     @Override
     public void handle(ActionEvent event) {
         // 获取控制器
-        Controller controller = new Controller();
+        Controller controller = Controller.getInstance();
         // 创建文件选择器
         FileChooser fileChooser = new FileChooser();
         // 显示文件选择对话框，并获取选中的文件

src/main/java/org/jcnc/jnotepad/controller/manager/Controller.java

@@ -26,6 +26,16 @@ import java.util.List;
  */
 public class Controller implements ControllerInterface {
 
+    private static final Controller INSTANCE = new Controller();
+
+    private Controller() {
+
+    }
+
+    public static Controller getInstance() {
+        return INSTANCE;
+    }
+
     /**
      * 打开关联文件并创建文本区域。
      *
@@ -271,7 +281,7 @@ public class Controller implements ControllerInterface {
         TextArea textArea = new TextArea();
         textArea.setStyle(
                 "-fx-border-color:white;" +
-                "-fx-background-color:white"
+                        "-fx-background-color:white"
         );
         return textArea;
     }

src/main/java/org/jcnc/jnotepad/view/init/View.java

@@ -21,17 +21,17 @@ public class View {
 
     public void initItem() {
         // 初始化菜单项的事件处理器
-        EventHandler<ActionEvent> newFileEventHandler = new Controller().getNewFileEventHandler(new TextArea());
+        EventHandler<ActionEvent> newFileEventHandler = Controller.getInstance().getNewFileEventHandler(new TextArea());
         newItem.setOnAction(newFileEventHandler);
-        EventHandler<ActionEvent> openFileEventHandler = new Controller().getOpenFileEventHandler();
+        EventHandler<ActionEvent> openFileEventHandler = Controller.getInstance().getOpenFileEventHandler();
         openItem.setOnAction(openFileEventHandler);
-        EventHandler<ActionEvent> saveAsFileEventHandler = new Controller().getSaveAsFileEventHandler();
+        EventHandler<ActionEvent> saveAsFileEventHandler = Controller.getInstance().getSaveAsFileEventHandler();
         saveAsItem.setOnAction(saveAsFileEventHandler);
-        lineFeedItem.setOnAction(new Controller().getLineFeedEventHandler(new TextArea()));
+        lineFeedItem.setOnAction(Controller.getInstance().getLineFeedEventHandler(new TextArea()));
     }
 
     public void initTabPane() {
-        new Controller().initTabPane();
+        Controller.getInstance().initTabPane();
     }
 
     // 初始化快捷键