Question

I’m doing my homework on java I/O data, the problem is i’m not allowed to use object serialization to load data from a binary file.

Here is the assignment requirements:

Persistence, writing objects to file and reading objects from file (Text format)

• All objects should be written to a single file in a text format
• All objects should be read form the same file
• You should use JFileChooser

I have 3 classes: Unit, Assessment, and Task.

The Assessment class is abstract while IndividualAssessment & GroupAssessment are concrete subclasses.

Unit has a collection of Assessment and Assessment has a collection of Tasks.

I could save all data to one text file with FileWriter but I don’t know how to read each line of the text file in to the proper Assessment class.

What I mean is how do you recognize which line is for IndividualAssessment or GroupAssessment classes.

Here is the code I tried but it’s not working:

BufferedReader bf = new BufferedReader(file);
While (bf.readLine != null){
    Unit u = new Unit(bf);
    diary.add(u);
    try{
        Assessment a = new IndividualAssessment(bf);
    } catch (IOException ex){
        Assessment a = new GroupAssessment(bf);
            }
    u.add(a);
    Task t = new Task(bf);
    a.add(t);

Answer 1

You should probably start with storing the content of the line you read in a String object. So it would look something like this:

String line = bf.readLine();
while(line != null) {
    // Add code to look at your line to figure out what kind of object it 
    // represents.   For example you could add a one character prefix to each 
    // line when you write it to specify which object it is ('U', 'A' or 'T').
    // Based on that, you can call a constructor of the appropriate object that
    // takes a String as input. Then let the constructor deal with parsing the
    // line for the object it represents. This way you don't end up with some
    // massive parsing routine.

    char code = line.charAt(0);
    if(code == 'T') {
        Task task = new Task();
        task.initFromString(line.sustring(1));
        ... Do something with your task
    }
    else if(code == ...) {
    }

    line = bf.readLine();    // Read the next line
}

Define some interface that all your object should implement:

public interface TextExportable {
    public char getClassIdentifier();
    public void initFromString(String s);
}

I’m not sure what your objects look like but let’s say for example:

public class Task implements TextExportable {
    private String name;

    public Task() {} // For the pseudo-serialization

    public Task(String name) { // For creating the object by hand
        this.name = name;
    }

    public char getClassIdentifier() {
        return 'T';
    }

    public String toString() {
        return getClassIdentifier()+name;
    }

    public void initFromString(String line) {
        this.name = line;
        // Here, you would need extra parsing if you have more than one attribute
        // and dissect the line
    }
}