Concepts of Programming Languages

14.4 Exception Handling in Java 651

A method that does not include a throws clause cannot propagate any

checked exception. Recall that in C++, a function without a throw clause can

throw any exception.

A method that calls a method that lists a particular checked exception in its

throws clause has three alternatives for dealing with that exception: First, it can

catch the exception and handle it. Second, it can catch the exception and throw

an exception that is listed in its own throws clause. Third, it could declare

the exception in its own throws clause and not handle it, which effectively

propagates the exception to an enclosing try clause, if there is one, or to the

method’s caller, if there is no enclosing try clause.

There are no default exception handlers, and it is not possible to disable

exceptions. Continuation in Java is exactly as in C++.

14.4.5 An Example

Following is the Java program with the capabilities of the C++ program in

Section 14.3.5:

// Grade Distribution

// Input: A list of integer values that represent

// grades, followed by a negative number

// Output: A distribution of grades, as a percentage for

// each of the categories 0-9, 10-19,.. .,

// 90-100.

import java.io.*;

// The exception definition to deal with the end of data

class NegativeInputException extends Exception {

public NegativeInputException() {

System.out.println("End of input data reached");

} //** end of constructor

} //** end of NegativeInputException class

class GradeDist {

int newGrade,

index,

limit_1,

limit_2;

int [] freq = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};

void buildDist() throws IOException {

DataInputStream in = new DataInputStream(System.in);

try {

while (true) {

System.out.println("Please input a grade");

newGrade = Integer.parseInt(in.readLine());

if (newGrade < 0)