Can we read/write different type child classes of the same parent class to a textfile?

Question

Suppose that I have an abstract class "Vehicle" and 2 other child classes inheriting from the Vehicle class called "Car" and "Bike".

So I can create a series of car and bike objects randomly:

Vehicle car = new Car();
Vehicle bike = new Bike();

And add them all to an Arraylist:

Arraylist<Vehicle> vehicles = new Arraylist<>();

Is it possible to write these objects to a single text file and also read it back from the text file to the Arraylist according to the specific object types(car, bike) without maintaining different textfiles for each type

Answer 1

If you want to store objects in a file, I'd advise you use object serialization. This link has useful details on how to serialise and deserialise a list

This is how you serialize a list:

ArrayList<Vehicle> vehicles= new ArrayList<>();
         
        vehicles.add(new Vehicle());
        vehicles.add(new Bike());
        vehicles.add(new Car());
 
        try
        {
            FileOutputStream fos = new FileOutputStream("vehiclesData");
            ObjectOutputStream oos = new ObjectOutputStream(fos);
            oos.writeObject(vehicles);
            oos.close();
            fos.close();
        } 
        catch (IOException ioe) 
        {
            ioe.printStackTrace();
        }

To deserialize use the following:

        ArrayList<Vehicle> vehicles= new ArrayList<>();
         
        try
        {
            FileInputStream fis = new FileInputStream("vehiclesData");
            ObjectInputStream ois = new ObjectInputStream(fis);
 
            vehicles= (ArrayList) ois.readObject();
 
            ois.close();
            fis.close();
        } 
        catch (IOException ioe) 
        {
            ioe.printStackTrace();
            return;
        } 
        catch (ClassNotFoundException c) 
        {
            System.out.println("Class not found");
            c.printStackTrace();
            return;
        }
         
        //Verify list data
        for (Vehicle vehicle : vehicles) {
            System.out.println(vehicle);
        }

Make sure all your classes implement serializable interface