Concepts of Programming Languages

14.4 Exception Handling in Java 647

catch(NegativeInputException& e) { //**Handler for

//** negative input

cout << "Limits Frequency" << endl;

for (index = 0; index < 10; index++) {

limit_1 = 10 * index;

limit_2 = limit_1 + 9;

if (index == 9)

limit_2 = 100;

cout << limit_1 << limit_2 << freq[index] << endl;

} //* end of for (index = 0)

} //* end of catch (NegativeInputException& e)

} //* end of main

This program is meant to illustrate the mechanics of C++ exception handling. Note

that the index range exception is often handled in C++ by overloading the indexing

operation, which could then raise the exception, rather than the direct detection of

the indexing operation with the selection construct used in our example.

14.3.6 Evaluation

In some ways, the C++ exception-handling mechanism is similar to that of

Ada. For example, unhandled exceptions in functions are propagated to the

function’s caller. However, in other ways, the C++ design is quite different:

There are no predefined hardware-detectable exceptions that can be handled

by the user, and exceptions are not named. Exceptions are connected to han-

dlers through a parameter type in which the formal parameter may be omitted.

The type of the formal parameter of a handler determines the condition under

which it is called but may have nothing whatsoever to do with the nature of the

raised exception. Therefore, the use of predefined types for exceptions certainly

does not promote readability. It is much better to define classes for exceptions

with meaningful names in a meaningful hierarchy that can be used for defining

exceptions. The exception parameter provides a way to pass information about

an exception to the exception handler.

14.4 Exception Handling in Java

In Chapter 13, the Java example program includes the use of exception

handling with little explanation. This section describes the details of Java’s

exception-handling capabilities.

Java’s exception handling is based on that of C++, but it is designed to be

more in line with the object-oriented language paradigm. Furthermore, Java

includes a collection of predefined exceptions that are implicitly raised by the

Java Virtual Machine ( JVM).