Question: How do I implement two interfaces in a class like so:

```
public class MainActivity extends Activity implements RewardedVideoAdListener implements GoogleApiClient.ConnectionCallbacks {
}

```

If it's impossible, what's the simplest workaround?

Answer: 
Simple 

```
public class MainActivity extends Activity implements RewardedVideoAdListener ,GoogleApiClient.ConnectionCallbacks {
}

```

Use a comma instead of implements.
Yes, you can just separate the classes it implements with commas rather than multiple `implements` keywords

```
public class MainActivity extends Activity 
   implements RewardedVideoAdListener, ConnectionCallbacks { }

```