Question: I have a question about declarative OSGi Services. I have the following interface : 

```
  public interface PrintService {
    public void print();
  }

```

and its implementation: 

```
    public class PrintServiceImpl implements PrintService {

      @Override
      public void print() {
        System.out.println("Hello from PrintServiceImpl!");
      }
    }

```

OSGI-INF/component.xml :

```
<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.1.0" name="service">
   <implementation class="service.PrintServiceImpl"/>
   <service>
      <provide interface="print.PrintService"/>
   </service>
</scr:component>

```

MANIFEST.MF :

```
Service-Component: OSGI-INF/component.xml

```

After I install the service and start it nothing happend. How can I activate it and print "*Hello from PrintServiceImpl!*" to console.

Answer: 
Why do you expect your `print` method to be invoked? It is part of the interface of the service, so it will not be invoked until you can a client that binds to it and calls it.

If you type the `services` command in the console you should see that your bundle is publishing the `print.PrintService` service; this means that your component is working. If you don't see this then you may be missing something like the SCR bundle as suggested by Tom Seidel in the comments above.
Did you ever get this working? For me it was that the Eclipse .ds bundle just hadn't started yet, and as such the service wasn't registered (yet). When I started it manually my service was registered correctly.