font android roboto

By - 
android:fontFamily="sans-serif"           // roboto regular
android:fontFamily="sans-serif-light"     // roboto light
android:fontFamily="sans-serif-condensed" // roboto condensed
android:fontFamily="sans-serif-thin"      // roboto thin (android 4.2)
android:fontFamily="sans-serif-medium"    // roboto medium (android 5.0)