Identifying and Correcting Common Java Programming

Errors And Misconceptions for Introductory Computer Science

Students

Maria HristovaAnanya MisraMegan Rutter

Advisor: Prof. Rebecca Mercuri 

Bryn Mawr College May 8th 2002

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

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.

Introduction

Background Proposal

Collaborative Research Experience for Women, Computer Research Association

Existing Projects DrScheme, BlueJ, Ready, JJ

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

Pea and Kurland – Cognitive Aspect

Du Boulay – Language-Independent Aspect

Fleury – Java Aspect

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

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)

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

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

Incorrect Semicolon in If Statement or For/While Loop

Semi-colon after if, for or while clause if (x == 0); {<statements>} instead of

if(x == 0) {<statements>} 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?

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);{<statements>} should be

Void methodName(arguments){<statements>} 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

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

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 ofint 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

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 ofsomeClass 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

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;}

}

Sample Run Outcome

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.

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

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.

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 <http://www. bluej.org/tutorial/tutorial.pdf>

Kolling, Michael. Why BlueJ? 22 January 2002 <http://www.bluej.org/why/why. html>PLT Scheme: Software: DrScheme Home Page. 22 January 2002 <http://www.plt-

scheme.org/software/drscheme/>TA Online: Common Java Compiler Errors. Department of Computer Science,

University of Arizona. 17 February 2002 <http:// www.cs.arizona.edu/people/teena/ ta_online/>