HANDLING EXCEPTIONS AND EVENTS - Java Programming: From Problem Analysis to Program Design - page 742

The constructors of the class es FileReader and PrintWriter that we used throw a
FileNotFoundException . Therefore, these constructors throw a checked exception.
When the compiler encounters the statements to open an input or output file, it checks
whether the program handles FileNotFoundExceptions , or reports them by throwing
them. Enabling the compiler to check for these types of exceptions reduces the number
of exceptions not properly handled by the program. Because our programs so far were
not required to handle FileNotFoundExceptions or other types of predefined excep-
tions, the programs handled the checked exceptions by throwing them. (Another
common checked exception that can occur during program execution is known as
IOExceptions . For example, the method read used in the Text Processing program-
ming example, in Chapter 9, may throw an IOException .)
When a program is being compiled, the compiler may not be able to determine whether
exceptions—such as division by zero, index out of bounds, or the next input is invalid—will
occur. Therefore, the compiler does not check these types of exceptions, called unchecked
exceptions. To significantly improve the correctness of programs, programmers must
check for these types of exceptions.
Because the compiler does not check for unchecked exceptions, the program does not
need to declare them using a throws clause or provide the code within the program
to deal with them. The exceptions belonging to a subclass of the class
RuntimeException are unchecked exceptions. Because InputMismatchException is a
subclass of the class RuntimeException , the exceptions thrown by the methods
nextInt and nextDouble are unchecked. Therefore, in all the programs that used the
methods nextInt and nextDouble , we did not use the throws clause to throw these
exceptions. If a program does not provide the code to handle an unchecked exception,
the exception is handled by Java's default exception handler.
In the method heading, the throws clause lists the types of exceptions thrown by the
method. The syntax of the throws clause is:

throws ExceptionType1, ExceptionType2, ...

where ExceptionType1 , ExceptionType2 , and so on, are the names of the exception
classes.
For example, consider the following method:
public static void exceptionMethod()
throws InputMismatchException, FileNotFoundException

{

//statements

}

The method exceptionMethod throws exceptions of type InputMismatchException
and FileNotFoundException .