select all added

src/FileMergerApp.java

@@ -26,13 +26,16 @@ public class FileMergerApp extends JFrame {
         textArea.setEditable(false);
 
         JButton selectButton = new JButton("Select");
+        JButton selectAllButton = new JButton("SelectAll");
         JButton mergeButton = new JButton("Merge");
 
         selectButton.addActionListener(e -> selectFiles());
+        selectAllButton.addActionListener(e -> selectAllFiles());
         mergeButton.addActionListener(e -> mergeFiles());
 
         JPanel buttonPanel = new JPanel();
         buttonPanel.add(selectButton);
+        buttonPanel.add(selectAllButton);
         buttonPanel.add(mergeButton);
 
         add(buttonPanel, BorderLayout.NORTH);
@@ -68,6 +71,57 @@ public class FileMergerApp extends JFrame {
         }
     }
     
+    private void selectAllFiles() {
+        JFileChooser chooser = new JFileChooser();
+
+        if (lastDirectory != null) {
+            chooser.setCurrentDirectory(lastDirectory);
+        }
+
+        chooser.setMultiSelectionEnabled(false);
+        chooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
+
+        int result = chooser.showOpenDialog(this);
+        if (result != JFileChooser.APPROVE_OPTION) {
+            return;
+        }
+        
+        File selectedDir = chooser.getSelectedFile();
+        if (selectedDir == null || !selectedDir.isDirectory()) {
+            return;
+        }
+        
+        lastDirectory = selectedDir;
+
+        List<File> files = new ArrayList<>();
+        collectFilesRecursively(selectedDir, files);
+
+        if (files.isEmpty()) {
+            return;
+        }
+        
+        for (File file : files) {
+            selectedFiles.add(file);
+            textArea.append(file.getAbsolutePath());
+            textArea.append(System.lineSeparator());
+        }
+    }
+    
+    private void collectFilesRecursively(File dir, List<File> result) {
+        File[] entries = dir.listFiles();
+        if (entries == null) {
+            return;
+        }
+
+        for (File entry : entries) {
+            if (entry.isDirectory()) {
+                collectFilesRecursively(entry, result);
+            } else {
+                result.add(entry);
+            }
+        }
+    }
+
     private void mergeFiles() {
         if (selectedFiles.isEmpty()) {
             JOptionPane.showMessageDialog(