Question

I am trying to read info from a file and create objects out of that information. Every 6 or so lines of the file is a different unit, meaning that the first set of lines are relevant to object A, the next set to object B, and so on.

I can read from the file and create my object just fine–for the first set. My problem is that I don’t know how to get the reader to pick up from the spot it left off at when creating the next object…

(Note: the read() method which creates the file is part of the new object being created, not in a main() or anything like that). Here are the relevant bits of code:

The driver:

public class CSD{

    public static void main (String[] argv){
        Vector V=new Vector(10);
        CoS jon=new CoS();
        jon.display();
    }//end main
}

which calls CoS, whose constructor is:

public CoS(){
    try{
        String fileName=getFileName();
        FileReader freader=new FileReader(fileName);
        BufferedReader inputFile=new BufferedReader(freader);
        this.read(inputFile);
        setDegree(major);
        setStatus(credits);
    } catch(FileNotFoundException ex){
    }//end catch
}

Which calls both read() and getFileName():

public void read(BufferedReader inputFile){
    try{
        int n;
        super.read(inputFile);
        String str=inputFile.readLine();
        if (str!=null){
            n=Integer.parseInt(str);
            setCredits(n);
            str=inputFile.readLine();
            setMajor(str);
        }//end if
    }catch(IOException ex){}
}//end method

public String getFileName() {
    Scanner scan = new Scanner(System.in);
    String filename;
    System.out.print("Enter the file name and path ==> ");
    filename = scan.nextLine();
    System.out.println("");
    return filename;
}

Thanks in advance, guys!

Answer 1

Why not use ObjectInputStream and ObjectOutputStream? Or any kind of real serialization?

javadoc: http://docs.oracle.com/javase/6/docs/api/java/io/ObjectOutputStream.html

example code: http://www.javadb.com/writing-objects-to-file-with-objectoutputstream

Basically, since you write your objects to a file and want to take care of the lines where they are located, I’ll suggest a few other serialization alternatives.

One is the Object * Stream – you create a ObjectStream on a File and just write objects thru it. Later when you read, you read the objects in the reverse order you wrote them and they will come back just as you wrote them.

Another is to implement Serializable. Remember that transient keyword? Use it on fields you do not want to save to the file.

And then there’s the raw “by hand” approach where you save only the things you want to save and reconstruct the objects later by passing these initialization values to their constructor. Kinda like people suggested that you make the file line a argument to the ctor 🙂

EDIT:
guess writing with Object*Streams requires you to implement Serializable or Externalizable.

but if the example code isn’t clear enough, ask 🙂