JAVA: Static Field in multiple classes + common interface

Question

Is there a way to setup the following construct in JAVA:

having a common interface or base class
having a static public field declared by the common interface
each model implementing the common interface should have its own static field (not one shared instance for all models)

Detailed explanation: I'm working with ORMLite and I need to refresh the ForeignCollections of my models after deserialization. For doing this I need to have a reference to my DAO from the models, which I don't want to.

So, I came up with the following concept:

keep a static field in each of the models of the following Interface:

public interface SerializableObserver {
  void onAfterDeserialization(Object object);
}

in my implementation of private void readObject(java.io.ObjectInputStream stream) throws IOException, ClassNotFoundException after reading in all ivars i'am calling the onAfterDeserialization-Method of the static field i'am holding in the model.
- In the Dao, I'm setting the static field of the model. So when the deserialization is finished, a method in my Dao is called. Where i can finally refresh the ForeignCollection so it's still valid after deserialization.

So what I'm looking for is some sort of way to make this whole approach a bit more generic so, I don't have to implement this behavior for all of my 20 Models. And finally, this is going to be an Android-App. so no fancy Java-8 things.

I don't understand your question. Though I found it somewhat interesting, can we move to chat? — Vimal Bera
– Vimal Bera, Commented Jul 2, 2017 at 7:05
That's what I've tried. But as far as I know I can't declare static fields or methods for an interface. — Sascha Held
– Sascha Held, Commented Jul 2, 2017 at 8:30

ESipalis · Accepted Answer · 2017-07-02 09:03:30Z

I would use another class that maps Model classes to SerializableObserver implementations. For example,

DeserializerMap:

public enum DeserializerMap {

    INSTANCE;

    private Map<Class<? extends Model>, SerializableObserver> modelObserverMap = new HashMap<>();

    public void registerSerializableObserver(Class<? extends Model> modelClass, SerializableObserver serializableObserver) {
        modelObserverMap.put( modelClass, serializableObserver );
    }

    public void deregisterSerializableObserver(Class<? extends Model> modelClass) {
        modelObserverMap.remove( modelClass );
    }

    public SerializableObserver getSerializableObserver(Class<? extends Model> modelClass){
        return modelObserverMap.get( modelClass );
    }

}

Model class:

public class ModelClass implements Model{

    private int id;

    public ModelClass(int id) {
        this.id = id;
    }

    private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException{
        ois.defaultReadObject();
        DeserializerMap.INSTANCE.getSerializableObserver( this.getClass() ).
                onAfterDeserialization( this );
    }
}

The "Model" interface just extends Serializable and is used in DeserializerMap, but you can just get rid of the interface and use Class<? extends Object> instead of Class<? extends Model> in DeserializerMap,

Model:

public interface Model extends Serializable{
}

DAO Class:

public class DAOClass {

    public DAOClass(){
        SerializableObserver serializableObserver = new SerializableObserver() {
            @Override
            public void onAfterDeserialization(Object object) {
                System.out.println("After deserialization");
                anotherMethod();
            }
        };
        DeserializerMap.INSTANCE.registerSerializableObserver( ModelClass.class, serializableObserver );
    }

    public void anotherMethod(){
        System.out.println("another method");
    }
}

if you don't want to do anything additional than just call DAOClass method then you can map ModelClass with DAOClass classes, but I would recommend using DAO just for communicating with your persistence system and register mappings in your main class and not in DAOClass constructor.

@SaschaHeld I've found your question on Upwork, could you accept a proposal?

Corneil du Plessis · Accepted Answer · 2017-07-02 08:16:35Z

0

Without understanding the details I can offer the following: Use an Interface to define commonly required behaviour and then a generic abstract base class to define a common structure is something you should consider.

answered Jul 2, 2017 at 8:16

Corneil du Plessis

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