Handling Errors Using Exceptions |
The previous section showed you how to write an exception handler for thewriteList
method in theListOfNumbers
class. Sometimes, it's appropriate for your code to catch exceptions that can occur within it. In other cases, however, it's better to let a method further up the call stack handle the exception. For example, if you were providing theListOfNumbers
class as part of a package of classes, you probably couldn't anticipate the needs of all of the users of your package. In this case, it's better to not catch the exception and to allow someone further up the call stack to handle it.If the
writeList
method doesn't catch the exceptions that can occur within it, then thewriteList
method must specify that it can throw them. Let's modify thewriteList
method to specify the methods that it can throw. To remind you, here's the original version of thewriteList
method:As you recall, thepublic void writeList() { System.out.println("Entering try statement"); int i; pStr = new PrintStream( new BufferedOutputStream( new FileOutputStream("OutFile.txt"))); for (i = 0; i < size; i++) pStr.println("Value at: " + i + " = " + victor.elementAt(i)); }new FileOutputStream("OutFile.txt")
statement might throw anIOException
(which is not a runtime exception). Thevictor.elementAt(i)
statement can throw anArrayIndexOutofBoundsException
(which, as a subclass ofRuntimeException
, is a runtime exception).To specify that
writeList
throws these two exceptions, you add athrows
clause to the method signature for thewriteList
method. Thethrows
clause is composed of thethrows
keyword followed by a comma-separated list of all the exceptions thrown by that method. Thethrows
clause goes after the method name and argument list and before the curly bracket that defines the scope of the method. Here's an example:Remember thatpublic void writeList throws IOException, ArrayIndexOutOfBoundsException {ArrayIndexOutofBoundsException
is a runtime exception, so you don't have to specify it in thethrows
clause, although you can.
Handling Errors Using Exceptions |