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This implementation uses an internal flag to track whether the exit is permitted. The method setExitAllowed() sets this flag. The checkExit() method throws a SecurityException when the flag is unset (that is, false). Because this flag is not initially set, normal exception processing bypasses the initial call to System.exit(). The program catches the SecurityException and performs mandatory cleanup operations, including logging the exception. The System.exit() method is enabled only after cleanup is complete.
Exceptions
ERR09-J-EX0: It is permissible for a command-line utility to call System.exit(), for example, when the required number of arguments are not input [Bloch 2008], [ESA 2005].
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