Exceptions - Java Software Solutions: Foundations of Program Design - page 550

We can define our own exceptions by deriving a new class from Exception or
one of its descendants. The class we choose as the parent depends on what situa-
tion or condition the new exception represents.
The program in Listing 11.5 instantiates an exception object and
throws it. The exception is created from the OutOfRangeException
class, which is shown in Listing 11.6. Note that this exception is not
part of the Java standard class library. It was created to represent the
situation in which a value is outside a particular valid range.

KEY CONCEPT
A new exception is defined by deriv-
ing a new class from the Exception
class or one of its descendants.

LISTING 11.5

//********************************************************************
// CreatingExceptions.java Author: Lewis/Loftus
//
// Demonstrates the ability to define an exception via inheritance.
//********************************************************************

import java.util.Scanner;

public class CreatingExceptions
{
//-----------------------------------------------------------------
// Creates an exception object and possibly throws it.
//-----------------------------------------------------------------
public static void main (String[] args) throws OutOfRangeException
{
final int MIN = 25, MAX = 40;

Scanner scan = new Scanner (System.in);

OutOfRangeException problem =
new OutOfRangeException ("Input value is out of range.");

System.out.print ("Enter an integer value between " + MIN +
" and " + MAX + ", inclusive: ");
int value = scan.nextInt();

// Determine if the exception should be thrown
if (value < MIN || value > MAX)
throw problem;

System.out.println ("End of main method."); // may never reach
}
}