1 INTRODUCTION  
2 BACKGROUND  
3 RELATED WORK  
4 METHODOLOGY  
5 RQ1: WHAT ARE THE TRENDS IN API RECOMMENDATION?  
6 RQ2: WHAT ARE THE COMMON DATA SOURCES IN API RECOMMENDATIONS?  
7 RQ3: WHAT ARE COMMON DATA PROCESSING TECHNIQUES APPLIED IN THE API RECOMMENDATION TOOLS?  
8 RQ4: WHAT ARE THE COMMON MODELING TECHNIQUES IN API RECOMMENDATION TOOLS?  
9 RQ5: WHAT ARE COMMON EVALUATIONS IN API RECOMMENDATION?  
10 CHALLENGES  
11 OPPORTUNITIES  
12 CONCLUSION