You should post your complete code. If you haven't attached the adView to your layout, you can do so in the following manner:
RelativeLayout.LayoutParams adViewParams = new RelativeLayout.LayoutParams(
RelativeLayout.LayoutParams.WRAP_CONTENT,
RelativeLayout.LayoutParams.WRAP_CONTENT);
adViewParams.addRule(RelativeLayout.CENTER_HORIZONTAL | RelativeLayout.ALIGN_PARENT_TOP);
RelativeLayout layout = new RelativeLayout(this);
layout.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,
LayoutParams.MATCH_PARENT));
AdRequest adRequest = new AdRequest.Builder().addTestDevice(AdRequest.DEVICE_ID_EMULATOR).build();
AdView adView = new AdView(this);
adView.setAdSize(AdSize.BANNER);
adView.setAdUnitId("some id here");
adView.loadAd(adRequest);
layout.addView(adView, adViewParams);
This solution assumes your layout is defined programatically. If your layout is defined via xml, you can use the Layout inflater to inflate it and attach the addView