Flow Control and Exception Handling - Exceptions

Definition:

An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions. (Sun tutorial: Handling Errors with Exceptions)

• exceptions provide a clean way to check for errors
• they are an explicit part of a methods contract

• exceptions are thrown at runtime if errors occur when a class is loaded or during method execution
• runtime exceptions are objects of the classes java.lang.RuntimeException, java.lang.Error or their subclasses
• runtime exceptions are also called unchecked exceptions

• code may also throw an exception using the throw statement
• these are non-runtime or checked exceptions
• any exceptions you create in your code should extend java.lang.Exception which implements the interface java.lang.Throwable
• you create your own exceptions to add useful data to an error message or, if you are interested in a particular error

• both forms of exceptions (checked and unchecked) may be caught and handled in exception-handling code
• an uncaught exception is caught by a default handler which halts execution and displays an error message
• exception handling is done using the try-catch-finally statment