How to replace first line of a text file in Java?

Question

Every time I implement the addVet method i need to replace the first line of the text file to include the number of objects. Here is my addVet method:

public static void addVet(Veterinarian newadd){
    Veterinarian.Vet.add(newadd); 
    try{
        try (PrintWriter write = new PrintWriter(new BufferedWriter(new FileWriter("VetList.txt",true)))) {
            write.println();
            write.print(newadd.getPetName());
            write.println();
            write.print(newadd.getBirthday());
            write.println();
            write.print(newadd.getSpecies());
            write.println();
            write.print(newadd.getBill());
            write.println();
            write.print(newadd.getOwner());
        }
    }
    catch (IOException cnw){
        System.err.println("file cannot be written into");
    }
}

I Don't know what method to use to write the file over. Here is the text file:

3
hopper
2003
kangaroo
555
Melody_harper
ketty
2009
cat
44
Kitty_katz
Spot
2005
Dog
333
Dottie_Marks

Thanks for the help

Answer 1

The object is creating a new file if none exists, if it does then it will call it. In the write() method put what you want to writ in the txt file. The close() method just signifies the end of writing on the file.

FileOutputStream object=new FileOutputStream("file.txt",true);
object.write(byte[]);
object.close();