Binary input in java 5

Question

Hi all, I'm working on a project for class and have come up against a problem and unfortunately my text is not with me... if anyone could help me out I'd be really grateful! My constructor for the MyStudents class looks like this:
public MyStudents(String inF, String outF) throws EOFException, IOException,
          ClassNotFoundException {
          ObjectInputStream fileInput = new ObjectInputStream
               (new FileInputStream (inF));
          outFilename = outF;
          nStudents = 0;
          int i = 0;
          while (true) {
               s[i] = new Student(fileInput.readUTF(), (Date) fileInput.readObject(), fileInput.readInt());
               i++;
               nStudents++;
     }In my main method, after asking the user to input the binary input file, I have this code:
          MyStudents myClass = null;
          try {
               myClass = new MyStudents(in, out);
          } catch (EOFException e) {
               System.out.println("EOFException");
          } catch (IOException e) {
               System.out.println("IOException");
          } catch (ClassNotFoundException e) {
               System.out.println("ClassNotFoundException");
          } catch (Exception e) {
               System.out.println(e.getMessage());
          System.out.println("Initial list of students...");
          myClass.toString();however then I am getting a null pointer exception when i do myClass.toString()... any thoughts as to why? Thanks!

Answer 1

Hmm .. where to start?
First of all it seems that you are using exceptions as a flow control mechanism, not really what they are intended for.
Secondly, when an exception is thrown in a constructor, the constructor does not finish and thus the object does not get constructed. It is never good to have a constructor throw exceptions, just handle the exception internally.
And lastly you're not closing the input stream.
Try replacing
while (true)with
while (fileInput.available() > 0)That said, your reading of objects is assuming that the file is of the correct form. If the file is not a series of UTF string, date object and integer you'll still have the same problem.