1. Identifying and Correcting Common Java Programming Errors And Misconceptions for Introductory Computer Science Students Maria Hristova Ananya Misra Megan Rutter Advisor: Prof. Rebecca Mercuri Bryn Mawr College May 8 th 2002

2. Overview Abstract Introduction Theoretical Framework Data Collection And Organization Finding And Testing Solutions Example Errors, Solutions And Tests Sample Run Conclusion And Future of The Project

3. Abstract The Java programming language is currently growing in popularity within the academic community, and as a result of this, a lot of colleges are converting their introductory Computer Science courses into Java. While Java is a very portable and web-compatible language, students often have a hard time mastering it. There have been some projects that were aimed to assist students in grasping Java’s conceptual framework, but many of these involved either simplified Java syntax or pre- constructed object modules that distanced students from the process of coding. Our goal was to design an educational tool that would identify common Java programming errors and misconceptions and facilitate the learning process, while making sure that the students interact directly with their code. In order to achieve our goal, we collected data from students, professors and members of the Special Interest Group on Computer Science Education, and compiled a list of errors we wanted our program to assess. We then created a multiple-pass preprocessor that detects these errors and suggests corrective action. This presentation discusses the process we experienced in identifying these errors, designing and coding solutions, and testing the resulting product.

4. Introduction Background Proposal Collaborative Research Experience for Women, Computer Research Association Existing Projects DrScheme, BlueJ, Ready, JJ

5. Theoretical Framework Pea and Kurland – Cognitive Aspect Define programming as both a mental mode and a skill like reading Define the need for a tight bond between an instructional and programming environment Du Boulay – Language-Independent Aspect Defines the five language-independent areas of difficulty and three kinds of corresponding mistakes Fleury – Java Aspect Creates a list of the four most common “student-constructed rules” in Java Explores how students understand Java code and what their misconceptions might be

6. Pea and Kurland – Cognitive Aspect

7. Du Boulay – Language-Independent Aspect

8. Fleury – Java Aspect

9. Data Collection Original List of Errors Professor Surveys US News and World Report’s Top 50 Liberal Arts Colleges 2002 SIGCSE Student Surveys Swarthmore College Student Essays Bryn Mawr and Haverford Colleges

10. Data Organization List of Errors Collected List of Errors Not Included in Final List Already Identified by Compiler Don’t Apply to Introductory Students Can’t Be Checked For Final List of Errors Considered by Our Program (on hand-out)

11. Designing and Testing Solutions Three Groups of Errors Syntax - errors in the spelling, punctuation and order of words in the program Semantic - errors that are likely to ensue from a mistaken idea of how the language interprets certain instructions Logic - errors that tend to arise from fallacious thinking by the programmer rather than from language peculiarities

12. Single Versus Double Equals Operator Assignment (=) versus Comparison (==) if( x = 0) instead of if(x == 0) int x == 1; instead of int x = 1; Solution Looks for the former in if, for and while clauses Looks for the latter everywhere else Problem: this solution misinterprets == in boolean expression outside selection and repetition structures

13. Incorrect Semicolon in If Statement or For/While Loop Semi-colon after if, for or while clause if (x == 0); { } instead of if(x == 0) { } Solution Locate if, for and while statements Possible error if there is a semi-colon directly after parentheses are balanced Special case: is the while keyword part of a do-while loop?

14. Incorrect Semicolon at the End of a Method Header There should never be a semicolon at the end of a method header Void methodName(arguments);{ } should be Void methodName(arguments){ } Solution Search through code for method headers If a method header is found, make sure there is not a semicolon before the opening curly bracket If a semicolon is found return an error

15. Invoking Methods With Wrong Arguments Method call parameter types must match method definition parameter types Given definition void methodName(int x, char y) in method call methodName(a, b) a must be an int and b must be a char Solution Store variables and their types in one vector and method names and their parameter types in another When method call is found in code, make sure its parameter types match those in vector If they don’t match, return an error Problems Multiple entries - will return false error Mismatched parameter types - will not detect error that is there Types don’t have to match exactly - a double can take an int

16. Invoking a Non-void Method as a Statement When a non-void method is called it returns a value of some type and it must be stored somewhere. For example: public int someMethod(){ int result;... return result;} is then being called as someMethod() instead of int someResultVariable = someMethod() Solution Store all method names Every time when there is a method call check to see if it is preceded by an operator like = or + or by ( If there is no variable that stores the return value an error message is returned

17. Class Declared Abstract Every Java interface being implemented in an applet requires that certain methods or adapters need to be present in the code even if they are empty For example: someClass extends Applet implements ActionListener{ public void init(){...}} instead of someClass extends Applet implements ActionListener{ public void init(){...} public void actionPerformed(ActionEvent e){...}} Solution Create a list that associates every interface with the appropriate methods or adapter If an interface is implemented, a search for the required components is performed If some methods or adapters are missing, an error message is returned

18. Sample Run Code // sample run import java.awt.*; import java.applet.*; import java.awt.event.*; public class SampleRun extends Applet implements ActionListener { Label sampleLabel = new Label("Sample Label", Label.LEFT); Panel samplePanel = new Panel(); public void init();{ samplePanel.setLayout(new FlowLayout(FlowLayout.LEFT)); samplePanel.add(sampleLabel); add(samplePanel); repaint(); } public void paint(Graphics g){ char bear = 'p'; String cheese = "appleSauce"; computeSum(cheese, bear); } public int computeSum(int apple, int sauce){ int appleSauce; if (apple = sauce){ appleSauce= apple + sauce; } else if (apple > sauce);{ appleSauce == apple - sauce; } else{ appleSauce = 49; } return appleSauce; }

19. Sample Run Outcome

20. Conclusion Our aim in this project was to create an educational tool that would not only help students identify and fix their existing programming errors, but also help prevent them from making them again in the future. We accomplished this by compiling a list of common Java programming errors made by introductory students, designing and coding a program that identifies these mistakes and returns instructive error messages, and testing our program on our test suite. We believe that our resulting project will prove to be a very useful tool for future introductory Computer Science students.

21. The Future of Our Project Assessment of the tool’s effectiveness in the classroom environment and examination of these results and student feedback to be reflected in future implementations Submission to Computer Science Education Journals for Publication Submission to SIGCSE Conference for Student Paper Presentation

22. Acknowledgements We would like to thank: * our families and friends for their support throughout this project * each other for the super team work, patience and understanding that made this project possible * Professor Rebecca Mercuri for her mentoring * the Computer Science department at Bryn Mawr College and especially Professor Deepak Kumar without whose enthusiasm and love for teaching none of us would be Computer Science majors * Anneliese Taylor who is the best science librarian that we know * Bryn Mawr College for establishing an environment where women can excel in science * and Collaborative Research Experience for Women, part of the Computer Research Association for their financial support with this project and their dedication to encouraging women in Computer Science.

23. Bibliography Du Boulay, Benedict. “Some Difficulties of Learning to Program.” Journal of Educational Computing Research Vol. 2(1). (1986): 57-73. Fleury, Ann. “Programming in Java: Student-Constructed Rules.” Proceedings of the Thirty-First SIGCSE Technical Symposium on Computer Science Education (2000): 197-201. Kurland, D. Midian and Roy D. Pea. “One the Cognitive Effects of Learning Computer Programming.” New Ideas in Psychology Vol.2 No.2. (1984): 137 – 168. Pea, Roy D. “Language-Independent Conceptual “Bugs” in Novice Programming.” Journal of Educational Computing Research Vol. 2(1). (1986): 25-36. Kolling, Michael. The BlueJ Tutorial Version 1.4. 23 January 2002 Kolling, Michael. Why BlueJ? 22 January 2002 PLT Scheme: Software: DrScheme Home Page. 22 January 2002 TA Online: Common Java Compiler Errors. Department of Computer Science, University of Arizona. 17 February 2002