The previous section showed how to write an exception
handler for the
writeList method in the
ListOfNumbers class. Sometimes, it's appropriate
for 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 the
ListOfNumbers class as part
of a package of classes, you probably couldn't anticipate
the needs of all the users of your package. In this case,
it's better to
not catch the exception and to allow a method
further up the call stack to handle it.
If the writeList method doesn't catch the checked
exceptions that can occur within it, the writeList
method must specify that it can throw these exceptions. Let's
modify the original writeList method to specify the
exceptions it can throw instead of catching them. To remind
you, here's the original version of the writeList
method that won't compile.
// Note: This method won't compile by design!
public void writeList() {
PrintWriter out =
new PrintWriter(new FileWriter("OutFile.txt"));
for (int i = 0; i < SIZE; i++) {
out.println("Value at: " + i + " = "
+ vector.elementAt(i));
}
out.close();
}
To specify that
writeList can throw two exceptions,
add a
throws clause to the method declaration
for the
writeList method. The
throws
clause comprises the
throws keyword followed by a
comma-separated list of all the exceptions thrown by that method.
The clause goes after the method name and argument list and before
the brace that defines the scope of the method; here's an example.
public void writeList() throws IOException,
ArrayIndexOutOfBoundsException {
Remember that
ArrayIndexOutOfBoundsException is an
unchecked exception; including it in the
throws clause is
not mandatory. You could just write the following.
public void writeList() throws IOException {
