Objective
In this lab you will practice writing and testing a recursive-descent parser to evaluate arithmetic expressions.
Setup
To get started, import the project for this lab, ExpressionEvaluator, from the ExpressionEvaluator.zip file available at this link. If you don't remember how to do this, see the Setup instructions in an earlier lab.
Method
- First carefully look through the file ExpressionEvaluator.java in the src folder and make sure you understand all the given members and the main method. Complete the body of the 5 static methods valueOfDigit, valueOfDigitSeq, valueOfFactor, valueOfTerm, and valueOfExpr comprising the parser by pasting the code you wrote for the homework into the skeleton provided.
- You can test your parser implementation in a couple different ways. Run the main program and enter valid expressions terminated by '!' or use the provided JUnit test fixture (in the test folder) to systematically test your parser. One sample test case is provided to show you how to set them up. Even though it may seem to be extra work, it is a good idea to write test cases of increasing complexity starting from very simple expressions. This will make the task of debugging your code much simpler than just typing "random" expressions in the main program or having to reenter the same expressions over and over again as you make changes to your code.
Additional Activities
- If you did not create a JUnit test plan because you tested using the main program provided and your code seemed to work, develop a test plan for the parser and write appropriate JUnit test cases to implement your plan. Run the fixture on your implementation of the parser and see whether it exposes any defects.
- Modify the grammar and the parser so that the evaluator allows the remainder operator (%) with the same precedence as multiplication (*) and division (/).