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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.
public void writeList() { PrintWriter out = new PrintWriter(new FileWriter("OutFile.txt")); for (int i = 0; i < SIZE; i++) { out.println("Value at: " + i + " = " + list.get(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, IndexOutOfBoundsException {
Remember that IndexOutOfBoundsException
is an unchecked exception; including it in the throws
clause is not mandatory. You could just write the following.
public void writeList() throws IOException {