Explain the differences between the key components Primary and Qualifier in these systems.

In the context of Java and, for example, frameworks like Spring, @Primary and @Qualifier are used to resolve ambiguities during dependency injection.

• @Primary marks one bean as the primary one, which will be used by default if there are multiple candidates of the same type.
• @Qualifier allows explicitly specifying which bean to inject, using a name or a special identifier.

Example:

@Component
@Primary
public class ServiceA implements Service {}

@Component
@Qualifier("specialService")
public class ServiceB implements Service {}

@Autowired
private Service service; // injects ServiceA

@Autowired
@Qualifier("specialService")
private Service service; // injects ServiceB

Thus, @Primary sets the preferred bean by default, and @Qualifier provides a precise choice of a specific bean.