Prefactoring

8.8. Dealing with Deviations and Errors

As discussed in Chapter 3, any system has to deal with deviations and errors. Deviations are those conditions that can be expected to occur in normal processing. Errors are those conditions resulting from hardware or software malfunctions.

8.8.1. Signaling Errors and Deviations

Tim and I separated the conditions that occur during processing into errors and deviations. We needed to decide how to signal each type of condition. Errors from hardware and software malfunctions are generally not expected, so exceptions provide a clean way to handle those conditions. To signal deviations some groups prefer using exceptions and other groups prefer using return values from methods. Tim and I chose exceptions, since that is the common paradigm in Java.

8.8.2. Deviation Conventions

The com.samscdrental.failures package contains deviations and exceptions:

    Deviation.java
    CDCategoryFormatDeviation.java
    CheckInDeviation.java
    CheckOutDeviation.java
    CustomerIDFormatDeviation.java
    DollarFormatDeviation.java
    ImportFileDeviation.java
    ImportFormatDeviation.java
    LateReturnDeviation.java
    NameFormatDeviation.java
    ParseLineDeviation.java
    PhysicalIDFormatDeviation.java
    PrinterFailureDeviation.java
    StatusDeviation.java
    UPCCodeFormatDeviation.java
    SeriousErrorException.java

To separate deviations from exceptions, all expected errors are derived from Deviation, which in turn is derived from Exception, the base class for Java exceptions. The Deviation object contains ...