Exploring Advanced Language Features - Beginning Java 7 - page 206

Althoughamethod'sreturnvaluemustbeexaminedtoseeifitrepresentsanexcep-
tion,errorcodesarealltooeasytoignore.Forexample,alazydevelopermightignore
thereturncodefrom Logger 's connect() methodandattempttocall log() .Ignor-
ingerrorcodesisonereasonwhyanewapproachtodealingwithexceptionshasbeen
invented.
Thisnewapproachisbasedonobjects.Whenanexceptionoccurs,anobjectrepres-
enting the exception is created by the code that was running when the exception oc-
curred. Details describing the exception's surrounding context are stored in the object.
These details are later examined to work around the exception.
Theobjectisthen thrown ,orhandedofftotheJVMtosearchfora handler ,codethat
canhandletheexception.(Iftheexceptionisanerror,theapplicationshouldnotprovide
ahandlerbecauseerrorsaresoserious[e.g.,theJVMhasrunoutofmemory]thatthere's
practicallynothingthatcanbedoneaboutthem.)Whenahandlerislocated,itscodeis
executed to provide a workaround. Otherwise, the JVM terminates the application.
Caution Codethathandlesexceptionscanbeasourceofbugsbecauseit'softennot
thoroughly tested. Always make sure to test any code that handles exceptions.
Apartfrombeingtooeasytoignore,anerrorcode'sBooleanorintegervalueisless
meaningfulthananobjectname.Forexample, fileNotFound isself-explanatory,but
whatdoes false mean?Also,anobjectcancontaininformationaboutwhatledtothe
exception. These details can be helpful to a suitable workaround.
The Throwable Class Hierarchy
Javaprovidesahierarchyofclassesthatrepresentdifferentkindsofexceptions.These
classesarerootedin java.lang.Throwable ,theultimatesuperclassforall throw-
ables (exception and error objects—exceptions and errors, for short—that can be
thrown). Table 3-1 identifies and describes most of Throwable 's constructors and
methods.