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14.6 Two Categories of Exceptions—Checked and Unchecked 565
public static int getIntFromUser()
{
Scanner stdIn = new Scanner(System.in);
String xStr;
// user entry
boolean valid = false; // is user entry a valid integer?
int x = 0;
// integer form of user entry
System.out.print("Enter an integer: ");
xStr = stdIn.next();
do
{
}
// end getIntFromUser
}
while (!valid);
try
{
}
}
x = Integer.parseInt(xStr);
valid = true;
catch (NumberFormatException nfe)
{
System.out.print("Invalid entry. Enter an integer: ");
xStr = stdIn.next();
return x;
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These initializations before the try block meet the compiler’s demands.
Figure 14.6 Corrected version of the getIntFromUser method
Identifying an Exception’s Category
How can you tell whether a particular exception is classified as checked or unchecked? An exception is an
object, and as such, it is associated with a particular class. To find out if a particular exception is checked
3
or unchecked, look up its associated class on Sun’s Java API Web site. Once you find the class, look at its
ancestors. If you find that it’s a descendant of the RuntimeExeption class, then it’s an unchecked excep- tion. Otherwise, it’s a checked exception.
For example, if you look up NumberFormatException on Sun’s Java API Web site, you’ll see this: java.lang.Object
java.lang.Throwable
java.lang.Exception
java.lang.RuntimeException
java.lang.IllegalArgumentException
java.lang.NumberFormatException
This shows that the NumberFormatException class is a descendant of the RuntimeException class, so the NumberFormatException class is an unchecked exception.
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