Handling Exceptions and Debugging - Beginning Java Programming: The Object-Oriented Approach - page 189

} catch (ArithmeticException ae){
System.out.println(ae);
System.exit(0);
}
The division and print statements will be attempted, but if an ArithmeticException is thrown, the
catch block will catch it. Then the exception will be printed and the program will be terminated.
Of course, you may prefer that the program not be terminated, but continue. You can change the
statements inside the catch block to accomplish this.
try {
double monthlyPension = retirementFund/yearsInRetirement/12;
System.out.println(name + " will have $" + monthlyPension
+ " per month for retirement.");
} catch (ArithmeticException ae){
System.out.println("Years in retirement should not be 0." +
"Default value is 20 years.");
double monthlyPension = retirementFund/20/12;
System.out.println(name + " will have $" + monthlyPension
+ " per month for retirement.");
}
Now if you run the program, it will try the original calculation, throw a division by 0 exception,
catch the exception in the catch block, and calculate the monthly pension using another non‐zero
value. This way, the program can execute fully.
You'll notice though, that the catch block was designed here to catch only exceptions of the
ArithmeticException type. You might have more than one exception type that must be handled.
In older versions of Java, you had two choices: create a separate catch block for each type of excep-
tion or catch all exceptions (or even all throwables , which include errors and exceptions, though this
is not advised) in one generic catch block. Since Java 7, you can catch more than one specific type of
exception in a single catch block.
try {
double monthlyPension = retirementFund/yearsInRetirement/12;
System.out.println(name + " will have $" + monthlyPension
+ " per month for retirement.");
} catch (ArithmeticException|NullPointerException exc){
System.out.println("Fields should not be null.");
System.out.println("Years in retirement should not be 0." +
"Default value is 20 years.");
double monthlyPension = retirementFund/20/12;
System.out.println(name + " will have $" + monthlyPension
+ " per month for retirement.");
}
You can see that if either of the specified exceptions is caught, the response in the catch block is
the same. In this particular case, you probably would prefer not to do this, since a null pointer
exception does not mean that the yearsInRetirement needs to be overwritten by the default
value. Therefore, it makes more sense to separate the two exceptions into two separate catch
blocks.