Cutting Java Expressions into Lines for Detecting their Evaluation at Runtime

Practical Java Debuggers can evaluate expressions at specified break points. Such evaluations may cause extra side effects and make an execution at debugging different from the original one. As a result, Java developers often have to edit the original source code in order to safely examine runtime values of expressions. In order to cope with this problem, we aim at developing a new feature for a debugger to detect evaluations of an expression by a Java virtual machine. This debugging feature doesn't introduce any extra side effects, and will enable Java programmers to examine runtime values of an expression by simply specifying it. The implementation of the above feature requires a debugger to make correspondence between bytecode instructions executed by a Java Virtual Machine and expressions in Java source texts. As the first step toward our goal, we have developed a source code translation method to make this correspondence using LineNumberTable attributes in class files generated by a standard Java compiler. There are still several cases that this method fails to automatically determine appropriate correspondence between bytecode instructions and expressions, but its solution has been left as future work. In this paper, we introduce a formalization to this method as a basis of our rigid analysis of failure cases. We evaluate our analysis method by conducting an experimental task to find failure patterns whose template is defined by our formalization.