Being a Java programmer and having worked for the top MNC in the world and having been associated with some apps, I have come to understand that just limiting your knowledge to programming will never make your money. May be you might get lucky to some what extent in freelancing. But the true money where you will be paid even when you are not working is apps.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.