DI.java

package rocks.biankouski.runinfiregame.desktop.opengl.service;

import java.util.Hashtable;
import java.util.Map;

public class DI {

    private final Map<Class<?>, Initializable> callbacks = new Hashtable<>();
    private final Map<Class<?>, Object> initiated = new Hashtable<>();

    public interface Initializable {
        Object init(DI di) throws NotDeclaredException;
    }

    public class NotDeclaredException extends Exception {
        NotDeclaredException(String message) {
            super(message);
        }
    }

    public void share(Class cls, Initializable callback) {
        callbacks.put(cls, callback);
    }

    public Object get(Class className) throws NotDeclaredException {
        Object instance = initiated.get(className);
        if (instance != null) {
            return instance;
        }

        Initializable initializable = callbacks.get(className);
        if (initializable == null) {
            throw new NotDeclaredException(className.getName() + " wasn't declared.");
        }

        instance = initializable.init(this);
        initiated.put(className, instance);

        return instance;
    }

}