Not sure why I'm getting an EOFException

Question

I'm trying to read objects from a file that I have written to but when reading there's an EOFException that gets thrown. I can see that it reads the objects but halfway through reading the file the error shows up.

public class IOStream {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws ClassNotFoundException {

        Person[] people = new Person[14];
        people[0] = new Professor("Professor", "Issac", "Newton", "Physcis", 6);
        people[1] = new TA("TA", "Marie", "Curie", "Physics", 6);
        people[2] = new Professor("Professor", "Issac", "Newton", "Calculus", 4);
        people[3] = new Student("Student", "Amy", "Adams", "Calculus", 4);
        people[4] = new Student("Student", "Will", "Smith", "Calculus", 4);
        people[5] = new Student("Student", "Brad", "Pitt", "Physics", 6);
        people[6] = new Student("Student", "Will", "Smith", "Physics", 6);
        people[7] = new Professor("Professor", "Dimitri", "Mendeleev", "Chemistry", 6);
        people[8] = new TA("TA", "Carl", "Gauss", "Calculus", 4);
        people[9] = new Student("Student", "Amy", "Adams", "Economics", 3);
        people[10] = new Professor("Professor", "Adam", "Smith", "Economics", 3);
        people[11] = new TA("TA", "Marie", "Curie", "Chemistry", 6);
        people[12] = new Student("Student", "Brad", "Pitt", "Chemistry", 6);
        people[13] = new Student("Student", "Will", "Smith", "Chemistry", 6);

        //WRITING
        try ( ObjectOutputStream out = new ObjectOutputStream(new BufferedOutputStream (new FileOutputStream("object.txt")))) {
            for (int i = 0; i < people.length; i++) {
                out.writeObject(people[i]);
            }
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        
        try (ObjectInputStream in = new ObjectInputStream(new BufferedInputStream( new FileInputStream("object.txt")))){
            
            
            Person lol;
            while ((lol = (Person)in.readObject())!= null){
                System.out.println(lol);
            }
        }
        catch(EOFException i){
            i.printStackTrace();
            System.out.println("End of File");
        }
        catch (IOException e){
            e.printStackTrace();
        } 
    }
}

Just a hint: don't use the `.txt` extension for files containing serialized data, because it will **not** be readable text in any meaningful way. I've seen `.ser` or `.obj` or `.dat` used, it's not that important, but `.txt` implies that the file contains human-readable text which is barely the case with these files. — Joachim Sauer, Jan 29 '23 at 14:31
Some remarks unrelated to the question: - you can declare and initialize an array in one go with the notation `Person[] people = { new Professor(), new TA(), new Student() }` (no need for indexes) - you don't need to manually close a stream in a [try-with-resources statement](https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html), so you can remove the call to `out.close()` - you can use the "for each" notation `for (Person p : people) { out.writeObject(p); }` instead of `for (int i = 0; i < people.length; i++) { out.writeObject(people[i]); }` for clarity — PotatoesMaster, Jan 29 '23 at 15:09

score 1 · Accepted Answer · answered Jan 29 '23 at 14:25

You get an EOFException because you've reached the End of the File.

For some reason you assume that in.readObject() will return null when it reached the end of the input, but that's not how it's specified.

You can either just use the EOFException as flow control (i.e. just let it happen in the flow of normal operation) or change to a format where you don't have to guess if more objects are available. The simplest way to do the second thing is to just write the whole array instead of individual people:

Replace your writing loop with just

out.writeObject(people);

And your reading loop with something like this:

Person[] readPeople = (Person[]) in.readObject();
for (int i = 0; i < readPeople .length; i++) {
    System.out.println(readPeople[i]);
}

Not sure why I'm getting an EOFException

1 Answers1