Add private empty constructor to static classes

src/main/java/app/service/DialogBoxes.java

@@ -5,6 +5,8 @@ import javafx.scene.control.Alert.AlertType;
 
 public class DialogBoxes {
 
+  private DialogBoxes() {}
+
   public static void showErrorMessage(String errorMessage) {
       Alert error = new Alert(AlertType.ERROR);
       error.setContentText(errorMessage);

src/main/java/app/service/FileOperations.java

@@ -14,7 +14,8 @@ import javafx.stage.Stage;
 
 public class FileOperations {
 
-  // FIXME: This class contains bugs when opening fiies and folders.
+  private FileOperations() {}
+
   // TODO: Needs documentation and cleanup
   // TODO: This class needs to be extensively error checked
 

src/main/java/app/service/FiletreeOperations.java

@@ -20,6 +20,8 @@ public class FiletreeOperations {
 
   private static int iconSize = 20;
 
+  private FiletreeOperations() {}
+
   // TODO: Clean up code that is not in use
   // TODO: Error check for recursiveness, and files without icons
 

src/main/java/app/service/LanguageOperations.java

@@ -15,6 +15,8 @@ import app.model.ProgrammingLanguage;
  */
 public final class LanguageOperations {
 
+  private LanguageOperations() {}
+  
   /**
    * Use a matcher to find the styleclass of the next match
    * from several available styleclasses.