The Sun Certified Java Developer Exam with J2SE 5: paper version from Amazon, PDF from Apress, Online reference: Books 24x7 Personal blog
"I'm not back." - Bill Harding, Twister
Can anybody explain what does it mean Exception chaining in jdk 1.4??? You can chain Exceptions in jdk 131 either (by re-throwing it!?)
(A throwable) can contain a cause: another throwable that caused this throwable to get thrown. The cause facility is new in release 1.4. It is also known as the chained exception facility, as the cause can, itself, have a cause, and so on, leading to a "chain" of exceptions, each caused by another.
One reason that a throwable may have a cause is that the class that throws it is built atop a lower layered abstraction, and an operation on the upper layer fails due to a failure in the lower layer. It would be bad design to let the throwable thrown by the lower layer propagate outward, as it is generally unrelated to the abstraction provided by the upper layer. Further, doing so would tie the API of the upper layer to the details of its implementation, assuming the lower layer's exception was a checked exception. Throwing a "wrapped exception" (i.e., an exception containing a cause) allows the upper layer to communicate the details of the failure to its caller without incurring either of these shortcomings. It preserves the flexibility to change the implementation of the upper layer without changing its API (in particular, the set of exceptions thrown by its methods).
A second reason that a throwable may have a cause is that the method that throws it must conform to a general-purpose interface that does not permit the method to throw the cause directly. For example, suppose a persistent collection conforms to the Collection interface, and that its persistence is implemented atop java.io. Suppose the internals of the put method can throw an IOException. The implementation can communicate the details of the IOException to its caller while conforming to the Collection interface by wrapping the IOException in an appropriate unchecked exception. (The specification for the persistent collection should indicate that it is capable of throwing such exceptions.)
A cause can be associated with a throwable in two ways: via a constructor that takes the cause as an argument, or via the initCause(Throwable) method. New throwable classes that wish to allow causes to be associated with them should provide constructors that take a cause and delegate (perhaps indirectly) to one of the Throwable constructors that takes a cause. For example:
Because the initCause method is public, it allows a cause to be associated with any throwable, even a "legacy throwable" whose implementation predates the addition of the exception chaining mechanism to Throwable. For example:
The Sun Certified Java Developer Exam with J2SE 5: paper version from Amazon, PDF from Apress, Online reference: Books 24x7 Personal blog
Do U really beleive that Sun will accept throwing Runtime Exception?
The Sun Certified Java Developer Exam with J2SE 5: paper version from Amazon, PDF from Apress, Online reference: Books 24x7 Personal blog
Consider Paul's rocket mass heater. |