Answer 1

Composition

public class Car {

private final Engine engine;

Car(EngineSpecs specs) {
engine = new Engine(specs);
}

void move() {
engine.work();
}
}

Aggregation

public class Car {

private Engine engine;

void setEngine(Engine engine) {
this.engine = engine;
}

void move() {
if (engine != null)
engine.work();
}
}