Error-Handling Overview

}Programsfrequently test conditions to determine how program execution should proceed. 

}Considerthe following pseudocode:

  §Performa task

If the preceding task did notexecute correctly
Perform error processing

Perform next task

  §If the preceding task did not execute correctly
Perform error processing

§…

–Begins by performing a task; then tests whether it executed correctly. –If not, perform error processing. 

–Otherwise, continue with the next task.

}Intermixing program and error-handling logic in this manner can make programs difficult toread, modify, maintain and debug—especially in large applications.

}Exception handling enables you to remove error-handling code from the “main line” of program execution

§Improves program clarity

§Enhances modifiability

}Handle any exceptions you choose

  §All exceptions

  §Allexceptions of a certain type 

  §All exceptions of a group of related types (i.e., related through a superclass). 

}Such flexibility reduces the likelihood that errors will be overlooked, thus making programs more robust.

}Exceptions are thrown(i.e., the exception occurs) when a method detects a problem and is unable to handle it. 

}Stacktrace—information displayed when an exception occurs and is not handled. 

}Information includes:

  §The name of the exception in a descriptive message that indicates the problem that occurred 

  §The method-call stack (i.e., the call chain) at the time it occurred. Represents the path of execution that led to the exception method by method.

}This information helps you debug the program. 

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