  Code comment generation is a crucial task in the field of automatic software
development. Most previous neural comment generation systems used an
encoder-decoder neural network and encoded only information from source code as
input. Software reuse is common in software development. However, this feature
has not been introduced to existing systems. Inspired by the traditional
IR-based approaches, we propose to use the existing comments of similar source
code as exemplars to guide the comment generation process. Based on an open
source search engine, we first retrieve a similar code and treat its comment as
an exemplar. Then we applied a seq2seq neural network to conduct an
exemplar-based comment generation. We evaluate our approach on a large-scale
Java corpus, and experimental results demonstrate that our model significantly
outperforms the state-of-the-art methods.
