You have two options:
1) Use stable Retrofit 1
This has the RestAdapter
class you need.
compile 'com.squareup.retrofit:retrofit:1.9.0'
2) Migrate to Retrofit 2
The RestAdapter
class was renamed to Retrofit
and the API was completely remade. Read more in Jake Wharton’s presentation.
compile 'com.squareup.retrofit:retrofit:2.0.0-beta1'
As of June 30 2016 the latest version is 2.1.0 obtained by
compile 'com.squareup.retrofit2:retrofit:2.1.0'
Please check http://square.github.io/retrofit/ for updates.