Retrofit cancellable callback

ECallback.java

import retrofit.Callback;
import retrofit.RetrofitError;
import retrofit.client.Response;

public class ECallback<T> implements Callback<T> {

    private Callback<T> callback;

    private boolean canceled;

    private ECallback() {}

    public ECallback(Callback<T> callback) {
        this.callback = callback;
        canceled = false;
    }

    public void cancel() {
        canceled = true;
        callback = null;
    }

    @Override
    public void success(T o, Response response) {
        if (!canceled) {
            callback.success(o, response);
        }
    }

    @Override
    public void failure(RetrofitError error) {
        if (!canceled) {
            callback.failure(error);
        }
    }
}