litersOfPetrol = Float.parseFloat(df.format(litersOfPetrol));
System.out.println("liters of petrol before putting in editor : "+litersOfPetrol);
You print Float here
, that has no format at all.
To print formatted float, just use
String formatted = df.format(litersOfPetrol);
System.out.println("liters of petrol before putting in editor : " + formatted);