Bugs & Debugging - Testing 10 Bugs & Debugging - Testing

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

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

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

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

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

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

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

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

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

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

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

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

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); } ...

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

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

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

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

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