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: 
You should make explicit that you want you service to start when the bundle is started. Otherwise, it will be instantiated lazily, and give that no other service requires the PrintService, it will not be instantiated at all.

You can control your service lifecycle (with regard to the bundle lifecycle) using the attributes `enabled` and `immediate`. `enabled` is trivial: indicates whether your service is enabled or not when the bundle is started. `immediate` indicates whether this service is lazy ot not. `immediate="true"` will start your service *immediatly*, `immediate="false"` will apply lazy instantiation (i.e. wait until some other service requests this service as a dependency)

e.g.

```
<scr:component xmlns:scr="http://www.osgi.org/xmlns/scr/v1.1.0" name="PrintService"
activate="activate" 
deactivate="deactivate"
modified="modified"
enabled="true" 
immediate="true">

```

As Chris mentioned, if you want your service to do something when it's activated, you should add some code to the `activate` lifecycle method (note that the name of the method can be specified in the component descriptor like it was done explicitly above)

```
protected final void activate() {
    print();
}

```
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.