title: Update TextArea while executing processes
body: <p>i found out that my GUI starts to freeze after 3-4 seconds when I click the "start" button like "no response". When I keep on click the App, it's forced to shut down.<br>
  Now I want to prevent this but I got no clue how. Just as far as I know JavaFX runs in a Single Thread, therefore, to update my TextArea while the Methods are executing, I need to run these Methods in another Thread.<br>
  I hope someone can help me.</p>
  
  <p><strong>How does my project look like?</strong>  </p>
  
  <p>I got a FXML, a Controller, a Handler, a Transformer , also a Writer and a Reader class (which are used in the Handler class).<br>
  When I click the button, which is bind to a method in the Controller, an instance of Handler is created and this one calls the Reader to read in a text file, transformed to a List of Strings (line by line).<br>
  In addition, the lines are getting manipulated. After this, the Writer is used to creat a new file and write the new manipulated lines to this file.<br>
  It is also allowed to the user to refer to more than just one file.<br>
  What I want is that the textarea shows whenever the reader starts to read a file like "The file ... is being read".<br>
  Then append "The file ... is being manipulated" when Transformer comes to action and then<br>
  "The file ... is being written" when the new lines are written to the new file.  </p>
  
  <p><strong>Here is some code..</strong><br>
  <strong>Controller:</strong></p>
  
  <pre><code>public class FXMLDocumentController implements Initializable {
  
  @FXML
  private TextArea console;
  
  @FXML
  private void handleButtonAction(ActionEvent event) {
      System.out.println("You clicked me!");
      Handler hand = new Handler();
      hand.handle(files);
  }
  
  @Override
  public void initialize(URL url, ResourceBundle rb) {
      // TODO
  }    
  
  }
  </code></pre>
  
  <p><strong>Handler:</strong>  </p>
  
  <pre><code>public class Handler {
  
  public void handle(List&lt;String&gt; files) {
      for (String s : files) {
          List&lt;String&gt; ls = Reader.readFile(s);
          Writer.writeFile(Transformer.transform(ls));
      }
  }
  </code></pre>
  
  <p>How should I change my code to update the TextArea whenever a file is read, manipulated or written?</p>
  
  <p><strong><em>Info</em></strong>: I know the class Handler won't compile as I erased the initialization of the List "files" which contains Strings of file paths.  </p>
  
  <p>If I left out relevant information, feel free to ask.<br>
  I thank you in advance!</p>