title: How to conditionally use vendor-specific APIs for Android apps?
body: <p>With Android app stores offering marketplace-specific APIs, how do I build an Android app that conditionally uses vendor-specific libraries?  For example, Amazon offers their own In-App Purchase and "GameCircle" APIs.  Google has their own Licensing APIs, and now Ouya will have their own APIs for IAP and hardware controllers.</p>
  
  <p>With the proliferation of these vendor-specific SDKs it's becoming difficult to maintain several separate builds of my Android games.  I would like to know how to build my projects so that my code can just check at runtime for various APIs and use them if avaialble.  Something like</p>
  
  <pre><code>if (amazon api is available)
    // Do some amazon-specific stuff
  </code></pre>
  
  <p>At build-time I would link with ALL the libraries then upload the same universal app to each store.</p>