How do I implement dependency injection in Java?

How do I implement dependency injection in Java?

To implement dependency injection in Java, you can use frameworks like Spring or CDI. Would you like a code example?

Yes, please provide a simple code example.

Sure! Here's a basic example using Spring:

@Component
class Service {
    public void serve() {
        System.out.println("Service is serving...");
    }
}

@Component
class Client {
    private final Service service;

    @Autowired
    public Client(Service service) {
        this.service = service;
    }

    public void doSomething() {
        service.serve();
    }
}

public class Main {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        Client client = context.getBean(Client.class);
        client.doSomething();
    }
}

This code demonstrates constructor injection. Do you have any questions about it?

What if I want to use manual dependency injection instead?

If you prefer manual dependency injection, you can create instances of your classes and pass them to the constructor directly. Here's an example:

class Service {
    public void serve() {
        System.out.println("Service is serving...");
    }
}

class Client {
    private final Service service;

    public Client(Service service) {
        this.service = service;
    }

    public void doSomething() {
        service.serve();
    }
}

public class Main {
    public static void main(String[] args) {
        Service service = new Service();
        Client client = new Client(service);
        client.doSomething();
    }
}

This way, you have full control over the instantiation.