Android FileInputStream Code causes Crash

Question

I've solved my own issue but I don't know why my first attempt didn't work and I was hoping someone could tell me why. I was also hoping if someone could tell me if my final solution is a "good" one or not (by this I mean, is it efficient)?

This was my first attempt at reading an input file I had previously created:

private byte[] mInputData;
public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.second_view);
 Intent myIntent = getIntent();
 mFilename = myIntent.getStringExtra("FILENAME");
 mSplitSeq = myIntent.getStringExtra("SPLIT_SEQ");
 try {
 fis = openFileInput(mFilename);
 fis.read(mInputData);
 fis.close();
 } catch (FileNotFoundException e) {
 e.printStackTrace();
 } catch (IOException e) {
 e.printStackTrace();
 }

This is something I found online that actually worked:

public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.second_view);
 Intent myIntent = getIntent();
 mFilename = myIntent.getStringExtra("FILENAME");
 mSplitSeq = myIntent.getStringExtra("SPLIT_SEQ");
 try {
 fis = openFileInput(mFilename);
 BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
 String line = null, input="";
 while ((line = reader.readLine()) != null)
 mTimeStr += line;
 reader.close();
 fis.close();
 //fis.read(mInputData);
 } catch (FileNotFoundException e) {
 e.printStackTrace();
 } catch (IOException e) {
 e.printStackTrace();
 }

The error I received with my first implementation was a NullPointerException when calling the fis.read(mInputData) function.

Answer 1

I'm pretty sure it's because mInputData is never initialized. You'd need a line in there like mInputData = new byte[1000];. Instead, you're telling read() to give data to a reference that equals null, a NullPointerException.

• J2N: Ah, that makes sense. Is there a way to make the byte array dynamic? I guess the second solution is dynamic but it would be nice to be able to call a read function that reads all without looping.
• MattDavis: You could use int byteArraySize = new File(mFileName).length(). The length method on a File returns the size in bytes.
• J2N: Do you see anything wrong with the BufferedReader method? Or anything that would be exceptionally inefficient?
• MattDavis: I think that using BufferedReader is a good way to read input and I'd stick with that method. However, take a look at the accepted answer to this question: stackoverflow.com/questions/2492076/… You may want to use a StringBuilder instead of appending to a String.
• J2N: Thank you, that was a good read and I now understand (and am using) StringBuilder instead!