Automatic Refactoring for Complex Conditional Statements Based on Abstract Syntax Tree and Polymorphism

In order to solve the problems that complex conditional statements increase the complexity of program, and affect the understandability, testability, maintainability, and extendibility of existing code, a novel approach for automatic refactoring of complex conditional statements based on abstract syntax tree and polymorphism is proposed. The approach can be used to detect the refactoring opportunities for complex conditional statements and implement automatic refactoring. In this approach, the source code file is transformed to an abstract syntax tree at first; then all of the conditional statements are detected and the candidate statements which meet the preconditions are identified; and finally, the conditional statements are refactored automatically by introducing polymorphism, and each branch of the them is encapsulated into a subclass. Four projects are tested to identify refactoring opportunities and implement automatic refactoring. The results show that the precision of the identification algorithm for refactoring opportunities is 100%. Meanwhile, the approach can execute automatic refactoring correctly. The regression testing shows that none error is imported after refactoring. In addition, this approach has good efficiency and the execution time has a linear relationship with the size of system. It means that this approach can be used for projects of different scales.