gRPC StreamObserver in Java

class Observer implements StreamObserver<Bar> {
	@Override
	public void onNext(Foo foo) {
		System.out.println("Received: " + foo.toString());
	}
 
	@Override
	public void onCompleted() {
		System.out.println("RPC call completed");
	}
 
	@Override
	public void onError(Throwable throwable) {
		System.out.println("RPC call error: " + throwable.getMessage());
	}
}