1. Bugs & Debugging - Testing10
Bugs & Debugging - Testing

2. Previously Design a program Javadoc
Break the problem into smaller ones
It may help to do it several times to reduce the problem enough
Outlines
Javadoc
Industry standard for documenting Java code
Create documentation in HML format
Other format can be obtained
Doxygen can be used to get documentation in C++, Java and other langugaes

3. Overview Types of Errors When errors appear Compiler Errors
Run-time errors
Fixing errors
Testing - Find Errors

4. Types of Errors Syntax errors
Code that does not conform to the syntax of the programming language
Detected a compiling time
// Declaring variables
int iCounter = 0
int iValue;
iValue = ++iCounter; 1 2 3 4 5

5. Types of Errors Semantic errors Mistakes in the logic of the code
Legal language code but not what intended
Appear when running the code
Exceptions

6. When errors appear Compile-time errors Run-time errors
Appear when the code is compiled
Run-time errors
Appear when the code is running
Makes the code to behave different than expected
Could take long time before effects are seen
Logical errors are run-time errors
Some languages try to reduce the risk of this errors, Java is one of them

7. Compiler Errors Eclipse will show them with a read circle and a cross
Some information is provided
The point of the error may not be where the error was introduced
Unbalanced braces cannot be detected until the braces are closed – indexation helps to detect the point of the problem
Previous error may create other errors, “spurious” errors

8. Let see some using Eclipse!
Compiler Errors
Let see some using Eclipse!

9. Run-time errors
Java does not allow some code to avoid potential run-time errors
float fCostProduct1 = 12.50;
float fCostProduct2 = 30.10;
int iTotal = fCostProduct1 + fCostProduct2;
Potential run-time errors may be detected by Eclipse and are displayed with a yellow triangle with an exclamation mark
You should investigate them
Take the appropriate action to remove them

10. Run-time errors Cause: Lack of validation
An example would be when expected a number and provided a string
Remember the exercise to convert from Celsius to Fahrenheit the data is inputted as an string from the console and converted to a number
What happen if the user input a character not a digit?
An exception is thrown

11. Run-time errors RuntimeException ArithmeticException e.g. 10 / 0
NullPointerException
IndexOutOfBoundsException
...
See lecture 6
Exceptions s are a type of Throwable
RuntimeExceptions are a type of Exception

12. Run-time errors Other causes: External factors Internal factors
Out of memory
Insufficient i/o privileges
...
Internal factors
Arithmetic errors
Invalid operation, e.g. try to read beyond the end of a file
Try to access an object that doesn’t exist, e.g. null object
Attempt to read beyond the end of an array

13. Run-time errors Logical errors Causes a program to operate incorrectly
The program does not terminate abnormally or crash
The behaviour of the program is different that what was intended
Can be difficult to spot

14. Run-time errors 1 2 3 4 5 6 7 8 9 10 11 12
// Example of a logical error String strAnswer; System.out.println("Press 'y' to continue or any other key” + ” to terminate: "); strAnswer = Scanner.nextLine(); // Exit the program if the key 'y' is pressed if (strAnswer.charAt(0) == 'n') { // Terminate the application System.exit(0); } ...

15. Let see some using Eclipse!
Run-time errors
Let see some using Eclipse!

16. Fixing errors Need to know an error exists – find errors
Gather as much information as possible
Logging messages helps
Establish where the error happens in the code
Debugging is the process of locating the errors (bugs) in the code
Design the fix
Implement the fix
Test that the fix really fixes the problem

17. Let do some debugging using Eclipse!
Run-time errors
Let do some debugging using Eclipse!

18. Testing - Find Errors
Test to find errors (bugs) that may exist in the code
Different type of tests are conducted at different stages of a project
Tests intend to establish the compliance to the requirements
Errors should be reproducible!
Requirement to be able to locate them and fix
Information gathered required to reproduce it

19. Testing - Find Errors Create unit testing Run some simple examples
Test units of your code
Check if the unit does what it is expected
The units are methods
Use JUnit in Java
Run some simple examples
System test
Test the complete, integrated system to evaluate the compliance of the system – behave as expected
Customers – NOT GOOD