为什么在使用datainputstream，java，android时会得到0kb的文件？

Question

I'm really confused about why I get a 0kb file when I use that code showing below. As the instruction of Java website about this class, I should be worked. but... And I want to generate a sine wave and output its result in to a txt fill in double. That is the first step of my code, and I'm stuck in such simple problem. Maybe I was not pretty understand how to use class file and datastream as I learned from offical website.

public class audioplayThread implements Runnable {
private File file;
private FileOutputStream ops;
private BufferedOutputStream bos;
private DataOutputStream dos;
private double Omega;
private int f = 18*1000;
private double pi;
private int samplenumber = 84;      //Assume OFDM symbol has 64 real value and 
private static final int Encording = AudioFormat.ENCODING_PCM_16BIT; //Data size for each frame = 16 bytes
private static final int Sample_rate = 48000;                        //Sample rate = 48000 HZ
private static final int Channel = AudioFormat.CHANNEL_OUT_MONO;         //Set as single track
private static final int Buffersize = AudioTrack.getMinBufferSize(Sample_rate, Channel,Encording);
@Override
public void run() {
    // TODO Auto-generated method stub
    file = new File(Environment.getExternalStorageDirectory().getAbsoluteFile(),"mmm.txt");
    if(file.exists()){
        file.delete();
    }
    try {
        file.createNewFile();
    } catch (IOException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    try {
        /*Create a datastream*/
        ops = new FileOutputStream(file);
        bos = new BufferedOutputStream(ops);
        dos = new DataOutputStream(bos);
        /*Set sine wave parameter*/
        pi = Math.PI;
        Omega = 2*pi*f/Sample_rate;

        /*Build instance for audiotrack*/
        //AudioTrack at = new AudioTrack(AudioManager.STREAM_MUSIC,Sample_rate, Channel, Encording, Buffersize, AudioTrack.MODE_STREAM);

        /*build sine wave*/
        double[] buffer = new double[samplenumber];
        for(int i=0;i<samplenumber;i++){
            buffer[i] = Math.sin(Omega*i);
            dos.writeDouble(buffer[i]);

        }
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

}

Answer 1

The problem is that you're not closing the streams when you're done. They are buffering the data and don't automatically flush their content when they are destroyed so all data is lost.

Answer 2

1. You're getting empty output because you're never closing the output stream. It is buffered, and it will stay buffered until you flush or close it.
2. You're getting binary because you're calling writeDouble() . That's what it does. If you want strings, use a BufferedWriter or PrintWriter .

3. All this:

    if(file.exists()){ file.delete(); } try { file.createNewFile(); } catch (IOException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } 

   is not only unnecessary: it is wasteful. new FileOutputStream already does all that. You are doubling or tripling the overhead of creating a file; you are doing it non-atomically; and you are wasting both time and space. Remove it all.