NaiveBuilder.java

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.LinkedList;
import java.util.List;

public final class NaiveBuilder {
	public static <T> T build(Class<T> aClass) throws IllegalAccessException, InvocationTargetException, InstantiationException {
		Constructor<?> firstConstructor = aClass.getConstructors()[0];
		if (hasDependencies(firstConstructor)) {
			Object[] dependencies = resolve(firstConstructor);
			return newInstance(firstConstructor, dependencies);
		}
		return newInstance(firstConstructor);
	}

	private static <T> T newInstance(Constructor<?> firstConstructor, Object... dependencies) throws InstantiationException, IllegalAccessException, InvocationTargetException {
		return (T) firstConstructor.newInstance(dependencies);
	}

	private static Object[] resolve(Constructor<?> firstConstructor) throws IllegalAccessException, InstantiationException, InvocationTargetException {
		List<Object> dependencies = new LinkedList<>();

		for (Class<?> dependency : firstConstructor.getParameterTypes()) {
			dependencies.add(build(dependency));
		}

		return dependencies.toArray();
	}

	private static boolean hasDependencies(Constructor<?> firstConstructor) {
		return firstConstructor.getParameterTypes().length > 0;
	}

	public static void main(String[] args) throws IllegalAccessException, InstantiationException, InvocationTargetException {
		A instance = NaiveBuilder.build(A.class);
		System.out.println(instance);
	}
}

class A {
	private final B b;
	private final C c;

	public A(B b, C c) {
		this.b = b;
		this.c = c;
	}
}

class B {
	public B() {

	}
}

class C {
	private final D d;

	public C(D d) {
		this.d = d;
	}
}

class D {
	public D() {

	}
}