Java：BufferedWriter NullPointerException

Question

I am attempting to write a method that has to take in a Writer object and use that to provide output to a file. The current code I have is throwing a NullPointerException , presumably because either there is an error in how I am creating my BufferedWriter or else in some instances w (the Writer object) is being passed as null . I have no control over what is passed as w , and cannot change the exceptions that this method is able to throw.

My code is as follows:

public void write(Writer w, Stat s) throws IOException {
    try{
        BufferedWriter writeFile = new BufferedWriter(w);
        writeFile.write(s.getData());
        writeFile.flush();
    } catch (IOException e){
        ...
    }
}

Is there something I'm doing wrong?

(This assignment arises out of homework, but this question isn't the homework itself)

Answer 1

You need both Writer w and Stat s to be not null. Therefore you should reject them if they are null.

public void write(Writer w, Stat s) throws IOException {
   if (w == null)
       throw new IllegalArgumentException("writer is null");
   if (s == null)
       throw new IllegalArgumentException("stats is null");
   ...