1. Error Handling Tonga Institute of Higher Education

2. Fixing Errors • Bug – An error in a program. • Debug - To find and remove errors (bugs) from a software program. • Read the error! • Use the task list to quickly take you to the source of your error. • Try to fix the error yourself before asking for help. • If you ask for help, be able to describe what's going on. • The more experience you have with errors, the better you will be able to fix them in the future.

3. Compile Errors, Runtime Errors and Logical Errors • Compile Errors – Errors that are found during the compilation of a program • Your program is unable to compile • Runtime Errors – Errors that cause an abnormal termination of a program • Your program crashes • Logical Errors – Errors that are not found during the compilation of a program and do not cause an abnormal termination of the program • These are the most difficult to find and often result in very big problems. • You set an employees pay check to be $500,000 instead of $50,000

4. Common Compile Errors • Java is Case Sensitive • Any class, method or variable name must be written exactly the same. • Error Message: • cannot resolve symbol • Symbol – A class, method or variable name • A semicolon is required at the end of every statement • Error Message: • ’;’ expected • Brackets and Parenthesis must occur in matching pairs • Every time we open a bracket or parenthesis, we need to close it. • Error Message: • ‘}’ expected • ‘)’ expected

5. Common Compile Errors • Parenthesis must surround the condition in an IF Statement • Error Message: • ‘(’ expected • Must Initialize a Variable before using it • Error Message: • Variable <variablename> might not have been initialized • Must specify a return type for each method • Error Message: • Invalid method declaration; return type required • A method that returns something must have a return value specified. • Error Message: • Missing return statement

6. Common Compile Errors • A method that returns something must return the correct type • Error Message: • Incompatible types • A method that doesn’t return anything must not use the return keyword • Error Message: • Cannot return a value from method whose result type is void • Creating an overloaded method with the same signature • <signature> is already defined in <classname>

7. Common Runtime Errors • The Equality Operator (==) is different from the Assignment Operator (=) • The IF Statement will not function properly • Not calling System.Exit(0); • This is required to exit a graphical user interface • Not providing a way for Loops to end • The program will run forever • Not including a Break statement in a Switch statement • Undesired code will be run • Dividing a number by 0 • Error Message: • java.lang.ArithmeticException: / by zero

8. Java Error Handling • Java can gracefully handle runtime errors • Things you may want to do in your error handling • Display an error message • Allow user to contact technical support • Allow user to send error data to creator of software • Save data • Release any resources that are being used

9. Exceptions • Exception – An error that occurred that can be handled by Java • An exception is a class • When an exception occurs, we can do 2 things: • Ignore the exception • Handle the exception • Use Try/Catch/Finally structure

10. Try/Catch/Finally Structure • Use the Try/Catch/Finally structure to handle exceptions • You can catch all exceptions or a particular type of an exception • The finally structure is optional try { //Code that may cause an exception } catch (<type of exception> <exception variable name>) { //Code that handles the exception } finally { //Code to always run after the try or catch code is run }

11. Try/Catch/Finally Statement - 1 Code you are trying

12. Demonstration Try/Catch/Finally 1

13. Try/Catch/Finally Statement - 2 Catches specific exception Code you are trying Catches general exceptions

14. Demonstration Try/Catch/Finally 2