The rationale behind the hierarchy is as follows:
- Exception subclasses represent errors that a program can reasonably recover from. Except for RuntimeException and its subclasses (see below), they generally represent errors that a program will expect to occur in the normal course of duty: for example, network connection errors and filing system errors.
- Error subclasses represent "serious" errors that a program generally shouldn't expect to catch and recover from. These include conditions such as an expected class file being missing, or an OutOfMemoryError.
- RuntimeException is a further subclass of Exception. RuntimeException and its subclasses are slightly different: they represent exceptions that a program shouldn't generally expect to occur, but could potentially recover from. They represent what are likely to be programming errors rather than errors due to invalid user input or a badly configured environment.
