You don't need any Thread to update the progress bar status. You know the total no of bytes present in the file. Just calculate the percent done on the basis of bytes read.
public void redfile() {
try {
...
long totalLength = f1.length();
double lengthPerPercent = 100.0 / totalLength;
long readLength = 0;
System.out.println(totalLength);
while ((s = br.readLine()) != null) {
readLength += s.length();
progressBar_1.setValue((int) Math.round(lengthPerPercent * readLength));
...
}
progressBar_1.setValue(100);
fr.close();
} catch (Exception e) {
...
}
}