Exception Handling: A Deeper Look - Java: How to Program Early Objects - page 470

•A throw statement (p. 457) can throw any Throwable object.
• Exceptions are rethrown (p. 458) when a catch block, upon receiving an exception, decides ei-
ther that it cannot process that exception or that it can only partially process it. Rethrowing an
exception defers the exception handling (or perhaps a portion of it) to another catch block.
• When a rethrow occurs, the next enclosing try block detects the rethrown exception, and that
try block's catch blocks attempt to handle it.
Section 11.7 Stack Unwinding and Obtaining Information from an Exception Object
• When an exception is thrown but not caught in a particular scope, the method-call stack is un-
wound, and an attempt is made to catch the exception in the next outer try statement.
• Class Throwable offers a printStackTrace method that prints the method-call stack. Often, this
is helpful in testing and debugging.
• Class Throwable also provides a getStackTrace method that obtains the same stack-trace infor-
mation that's printed by printStackTrace (p. 461).
• Class Throwable 's getMessage method (p. 461) returns the descriptive string stored in an excep-
tion.
•Method getStackTrace (p. 461) obtains the stack-trace information as an array of StackTrace-
Element objects. Each StackTraceElement represents one method call on the method-call stack.
• StackTraceElement methods (p. 461) getClassName , getFileName , getLineNumber and get-
MethodName get the class name, filename, line number and method name, respectively.
Section 11.8 Chained Exceptions
• Chained exceptions (p. 462) enable an exception object to maintain the complete stack-trace in-
formation, including information about previous exceptions that caused the current exception.
Section 11.9 Declaring New Exception Types
• A new exception class must extend an existing exception class to ensure that the class can be used
with the exception-handling mechanism.
Section 11.10 Preconditions and Postconditions
• A method's precondition (p. 465) must be true when the method is invoked.
• A method's postcondition (p. 465) is true after the method successfully returns.
• When designing your own methods, you should state the preconditions and postconditions in a
comment before the method declaration.
Section 11.11 Assertions
• Assertions (p. 465) help catch potential bugs and identify possible logic errors.
•The assert statement (p. 466) allows for validating assertions programmatically.
• To enable assertions at runtime, use the -ea switch when running the java command.
Section 11.12 try -with-Resources: Automatic Resource Deallocation
•The try -with-resources statement (p. 467) simplifies writing code in which you obtain a resource,
use it in a try block and release the resource in a corresponding finally block. Instead, you allocate
the resource in the parentheses following the try keyword and use the resource in the try block;
then the statement implicitly calls the resource's close method at the end of the try block.
• Each resource must be an object of a class that implements the AutoCloseable interface
(p. 467)—such a class has a close method.