My university professor shared this class with us (it's essentially a generic parser using Gson): I created a class that inherits from it so I can read a Business from a file: Intellij automatically generated a constructor for it, but I don't understand it. Why does the constructor has a class as a parameter, do I have to pass an

How do I create a constructor for a class that is inheriting from an abstract class with generics?

My university professor shared this class with us (it’s essentially a generic parser using Gson):

public abstract class GenericDAO<T> {
    final Class<T> clase;
    protected File archivo;

    public GenericDAO(Class<T> clase, String file) throws Exception {
        this.clase = clase;
        this.archivo = new File(file);
        this.archivo.createNewFile();
    }

    public List<T> getAll(Class<T> clase) throws Exception {
        List<T> list = new ArrayList<T>();
        FileReader f = new FileReader(archivo);
        BufferedReader b = new BufferedReader(f);
        Gson g = new Gson();
        String line = "";

        try {

            while ((line = b.readLine()) != null && !line.equals("")) {
                JsonParser parser = new JsonParser();
                JsonObject jsonObject = parser.parse(line).getAsJsonObject();
                list.add(g.fromJson(jsonObject, clase));
            }
            b.close();
        } catch (Exception e) {
            e.printStackTrace();
            return list;
        }
        return list;
    }

    // a lot of other methods to read/write to json files
}

I created a class that inherits from it so I can read a Business from a file:

public class Business extends GenericDAO<Business> {
    private String name;
    // a lot of other members

    // this was automatically generated by Intellij:
    public Business(Class<Business> clase, String file) throws Exception {
        super(clase, file);
    }
}

Intellij automatically generated a constructor for it, but I don’t understand it. Why does the constructor has a class as a parameter, do I have to pass an instance of itself to it? That doesn’t make sense.

I would be grateful if you can point me to either some documentation to read through, or explain the pattern my professor is using.

Edit: to sum up, how do I instantiate my business class then? This is throwing an error:

 Business client = new Business(Business, "path_to_json_file.json");

Answer

This wouldn’t fit well in a comment: you could use a different style of constructor if you want. Replace this:

// this was automatically generated by Intellij:
public Business(Class<Business> clase, String file) throws Exception {
    super(clase, file);
}

With this:

public Business(String file) throws Exception {
    super( Business.class, file);
}

Which I think is more like your instructor may have intended.

Advertisement

Answer