“…On the one hand, API usability was studied through empirical experiments (e.g., [2,3,4,5,6]), which revealed the types of barriers that API users face (e.g., relationships between types and instantiation of abstract types). On the other hand, recommendation systems were proposed as an aid to assist API users through IDE (Integrated Development Environment) code completion mechanisms, which rely either on structural analysis (e.g., [7,8]) or on mining patterns from source code (e.g., [9,10,11,12,13]). Although code completion is an IDE feature that boosts programmer productivity with respect to code writing using a familiar API, empirical studies demonstrated that code completion is often used to explore, and hence, learn an unfamiliar API (e.g., [3,6]).…”