The need for the multithreading in javafx - multithreading

Question

I'm new to javafx and I have a question. My project is a voice browser with some simple command but I have an issue in switch(). The command at lines one and three of first case statement work, but line 2 does not. But if I remove the while loop, it works well! I have no idea how to solve this, help me please!
Here is my code
btSpeak.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
new Task<Void>(){
public Void call(){
int click=JOptionPane.showConfirmDialog(null, "Bạn đã sẵn sàng trải nghiệm với VoiceCommand chưa", "Speak", JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
if(click==JOptionPane.YES_OPTION) {
JOptionPane.showMessageDialog(null, "Start", "Speak", JOptionPane.INFORMATION_MESSAGE);
// code for voice recognize
try {
URL url;
url = HelloWorld.class.getResource("helloworld.config.xml");
System.out.println("Loading..."+url.toString());
ConfigurationManager cm = new ConfigurationManager(url);
final Recognizer recognizer = (Recognizer) cm.lookup("recognizer");
Microphone microphone = (Microphone) cm.lookup("microphone");
/* allocate the resource necessary for the recognizer */
recognizer.allocate();
/* the microphone will keep recording until the program exits */
if (microphone.startRecording())
{
System.out.println("Say: (Leen | Xuoongs| Trais | Phair | DDi |Veef| Dongs-Tab|Mowr-Tab| Noi - Dung| Trang-Chur|Trang-Truoc)") ;
System.out.println("Start speaking. Press Ctrl-C to quit.\n");
/*
* This method will return when the end of speech
* is reached. Note that the endpointer will determine
* the end of speech.
*/
// Platform.runLater(new Runnable(){
// public void run(){
int i = 0;
while(i< 5) {
//Thread.this.notifyAll();
Result result = recognizer.recognize();
if (result != null)
{
int t = 0;
System.out.println("Enter your choise"+ "\n");
resultText = result.getBestFinalResultNoFiller();
System.out.println("You said: " + resultText + "\n");
if(resultText.equals("xuoongs")) {
t = 1;
} else if(resultText.equals("leen")) {
t = 2;
}
switch(t) {
case 1: {
JOptionPane.showMessageDialog(null, "xuống");//line 1
webEngine.executeScript("window.scrollBy(0,100)");line 2
break;// line 3
}
case 2: {
JOptionPane.showMessageDialog(null, "lên");
webEngine.executeScript("window.scrollBy(0,-100)");
break;
}
}// end switch
}// end if
}//end while()
}// end if
} catch (PropertyException e) {
System.err.println("Problem configuring HelloWorld: " + e);
e.printStackTrace();
}
}
}
}.run());
}// end button
});