import java.io.*;
import javax.swing.*;

class WriteDataFile
{
    public static void main(String[] args)  throws IOException
    {
        String fname = JOptionPane.showInputDialog(null,"Enter file name");
        FileOutputStream myStream = new FileOutputStream(fname);
        DataOutputStream myDataStream = new DataOutputStream(myStream);

        double x = 23456.123456789086;
        double y = 456.123;

        myDataStream.writeInt(2);
        myDataStream.writeDouble(x);
        myDataStream.writeDouble(y);

        myDataStream.close();
        System.exit(0);
    }
}