ReInstancer: An Automatic Refactoring Approach for Instancerof Pattern Matching

Abstract

The extit{instanceof} pattern matching is periodically previewed in the latest published JDK by removing the redundant casting and optimizing its usage in different scenarios, which improves the code quality and readability. However, the existing integrated development environment (IDE) does not provide sufficient support for refactoring of extit{instanceof} pattern matching in all situations. This paper first identifies several cases that cannot be handled by existing IDEs, and then proposes a novel approach called extit{ReInstancer} to refactor extit{instanceof} pattern matching automatically. extit{ReInstancer} conducts visitor pattern analysis for extit{if} statement blocks with extit{instanceof}. For the extit{instanceof} expression, a pattern variable is obtained after removing the redundant type casting by pattern analysis. For multi-branch statements, extit{ReInstancer} employs class hierarchy analysis and control flow analysis to infer the relationship of instance type in each branch and then optimize these branches. Finally, the multi-branch statements are converted into switch statements or switch expressions. extit{ReInstancer} is evaluated with 20 real-world applications. The experimental results demonstrate a total of 3558 extit{instanceof} expressions and 228 multi-branch statements applying the refactoring, and each application takes an average of 10.8s. extit{ReInstancer} not only reduces the redundant type casting but also improves the code quality.