diff --git a/build/VocabularyDecoder.jar b/build/VocabularyDecoder.jar
index fef29c3..57b2bce 100644
Binary files a/build/VocabularyDecoder.jar and b/build/VocabularyDecoder.jar differ
diff --git a/src/main/java/xyz/scottc/Main.java b/src/main/java/xyz/scottc/Main.java
index b401324..c941c7c 100644
--- a/src/main/java/xyz/scottc/Main.java
+++ b/src/main/java/xyz/scottc/Main.java
@@ -13,12 +13,12 @@ public static void main(String[] args) {
     }
 
     private static void initFrame() {
-/*        try {
+        try {
             UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
         } catch (ClassNotFoundException | InstantiationException | UnsupportedLookAndFeelException |
                 IllegalAccessException e) {
             e.printStackTrace();
-        }*/
+        }
         MainFrame frame = new MainFrame("Vocabulary Decoder");
         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         frame.setSize(new Dimension(1000, 1000));
diff --git a/src/main/java/xyz/scottc/frames/commonModeFrame/component/LeftPanel.java b/src/main/java/xyz/scottc/frames/commonModeFrame/component/LeftPanel.java
index 0fcf2a0..0dec7f1 100644
--- a/src/main/java/xyz/scottc/frames/commonModeFrame/component/LeftPanel.java
+++ b/src/main/java/xyz/scottc/frames/commonModeFrame/component/LeftPanel.java
@@ -11,9 +11,12 @@
 import java.awt.event.MouseAdapter;
 import java.awt.event.MouseEvent;
 import java.io.*;
+import java.nio.file.Files;
+import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.Enumeration;
 import java.util.List;
+import java.util.Objects;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
 
@@ -47,8 +50,10 @@ public LeftPanel(CommonModeFrame parent, FunctionPanel functionPanel, TopPanel t
         this.setLayout(new CommonModeTopPanelLayout());
 
         this.add(this.importButton);
+        this.importButton.setToolTipText("Import the customized VD File which can be acquired by using \"Tools\" menu in the Main windows.");
         this.importButton.addActionListener(e -> this.importFile());
         this.add(this.exportButton);
+        this.exportButton.setToolTipText("Export your answer report.");
 
         this.add(this.internalFileListLabel);
         this.add(this.internalFileListScrollPane);
@@ -76,6 +81,7 @@ public void mouseClicked(MouseEvent e) {
 
         //backButton
         this.add(this.backButton);
+        this.backButton.setToolTipText("Go back to the Main windows.");
         this.backButton.addActionListener(e -> this.goBackToMainFrame());
     }
 
@@ -128,23 +134,6 @@ private void addExternalVocabularyPool() {
     }
 
     private void addInternalVocabularyPool() {
-        //create the InternalLibrary directory
-        File directory = FileUtils.getDirectoryFile(this);
-        File internalLibrary = new File(directory.getAbsolutePath() + "/InternalLibrary");
-        if (internalLibrary.exists()) {
-            for (File file : internalLibrary.listFiles()) {
-                boolean success = file.delete();
-                if (!success) {
-                    System.out.println("File deleting in InternalLibrary Fail!");
-                }
-            }
-        } else {
-            boolean success = internalLibrary.mkdir();
-            if (!success) {
-                System.out.println("Creating InternalLibrary Fails!");
-            }
-        }
-
         //copy the internal json file to the InternalLibrary directory
         String jarPath = FileUtils.getJarFilePath(this);
         JarFile jarFile;
@@ -157,16 +146,9 @@ private void addInternalVocabularyPool() {
                 String innerPath = jarEntry.getName();
                 if (innerPath.startsWith(internalPath) && !innerPath.equals(internalPath)) {
                     InputStream inputStream = this.getClass().getResourceAsStream("/" + innerPath);
-                    String target = internalLibrary.getAbsolutePath() + innerPath.substring(28);
-                    OutputStream outputStream = new FileOutputStream(target);
-                    int length;
-                    byte[] buffer = new byte[1024];
-                    while ((length = inputStream.read(buffer)) != -1) {
-                        outputStream.write(buffer, 0, length);
-                    }
-                    outputStream.flush();
+                    String target = MainFrame.internalLibrary.getAbsolutePath() + innerPath.substring(28);
+                    Files.copy(inputStream, Paths.get(target));
                     inputStream.close();
-                    outputStream.close();
                 }
             }
         } catch (IOException e) {
@@ -174,7 +156,7 @@ private void addInternalVocabularyPool() {
         }
 
         //add all the file in InternalLibrary directory to list
-        for (File file : internalLibrary.listFiles()) {
+        for (File file : Objects.requireNonNull(MainFrame.internalLibrary.listFiles())) {
             this.internalVocabularyPool.add(file);
             this.internalFileListModel.addElement(file.getName());
         }
diff --git a/src/main/java/xyz/scottc/frames/mainFrame/MainFrame.java b/src/main/java/xyz/scottc/frames/mainFrame/MainFrame.java
index d6bd148..da0f4d5 100644
--- a/src/main/java/xyz/scottc/frames/mainFrame/MainFrame.java
+++ b/src/main/java/xyz/scottc/frames/mainFrame/MainFrame.java
@@ -9,6 +9,7 @@
 import java.awt.*;
 import java.awt.event.ActionListener;
 import java.io.File;
+import java.util.Objects;
 
 public class MainFrame extends JFrame {
 
@@ -32,6 +33,8 @@ public class MainFrame extends JFrame {
 
     public boolean isExternalLibraryExist = false;
     public static File externalLibrary;
+    public boolean isInternalLibraryExist = false;
+    public static File internalLibrary;
 
     public MainFrame(String title) throws HeadlessException {
         super(title);
@@ -73,18 +76,44 @@ private void menuBarHandler() {
         this.inputToJson.addActionListener(this.inputToJsonListener);
     }
 
+    //Initialize the directories required for internal and external vocabularies list.
     private void initialize() {
         File directory = FileUtils.getDirectoryFile(this);
-        File[] files = directory.listFiles();
-        externalLibrary = new File(directory.getAbsolutePath() + "/ExternalLibrary");
-        for (File file : files) {
-            if (file.isDirectory() && "ExternalLibrary".equals(file.getName())) {
-                this.isExternalLibraryExist = true;
+        if (directory != null) {
+            File[] files = directory.listFiles();
+            if (files != null) {
+                externalLibrary = new File(directory.getAbsolutePath() + "/ExternalLibrary");
+                internalLibrary = new File(directory.getAbsolutePath() + "/InternalLibrary");
+                for (File file : files) {
+                    if (file.isDirectory() && "ExternalLibrary".equals(file.getName())) {
+                        for (File subFile : Objects.requireNonNull(file.listFiles())) {
+                            boolean success = subFile.delete();
+                            if (success) System.out.println("File deletion failed");
+                        }
+                        this.isExternalLibraryExist = true;
+                    }
+                    if (file.isDirectory() && "InternalLibrary".equals(file.getName())) {
+                        for (File subFile : Objects.requireNonNull(file.listFiles())) {
+                            boolean success = subFile.delete();
+                            if (success) System.out.println("File deletion failed");
+                        }
+                        this.isInternalLibraryExist = true;
+                    }
+                }
+                if (!this.isExternalLibraryExist) {
+                    boolean success = externalLibrary.mkdir();
+                    if (!success) {
+                        System.out.println("Creating ExternalLibrary Fails!");
+                    }
+                }
+                if (!this.isInternalLibraryExist) {
+                    boolean success = internalLibrary.mkdir();
+                    if (!success) {
+                        System.out.println("Creating InternalLibrary Fails!");
+                    }
+                }
             }
         }
-        if (!this.isExternalLibraryExist) {
-            boolean success = externalLibrary.mkdir();
-        }
     }
 
     private final ActionListener txtToJsonListener = e -> {