🚀 go-pugleaf

Hi I have the following problem:
I want to read a file with an DataInputStream, modify each byte and write
the modified file to another file.
Here I want  to use the JProgressBar to show the progress of the method.
But the JProgressBar does not get updated, until everything is finished!
What's the problem?
Here's the code of the method:

public static void kodiere(String quelldatei,String zieldatei) throws
IOException {
    FileInputStream quellenlaenge = new FileInputStream(quelldatei);
   int i,laenge= (int) quellenlaenge.available();
   DataInput quelle = new DataInputStream(new
FileInputStream(quelldatei));
  DataOutput ziel = new DataOutputStream(new
FileOutputStream(zieldatei));


  System.out.println(laenge);


for (i=0;i<laenge;i++){
byte b = (byte) quelle.readByte(); //Einlesen eines Bytes aus der
Quelle
       b = (byte) ((b+3)%256);
ziel.writeByte(b);
   JProgressBar jProgressBar1 = new JProgressBar();
   jProgressBar1.setValue(i); }


  }