An exception is an event, which is not expected to occur in the normal operation of a program. When an exceptional condition causes an exception to be thrown, that exception is an object derived, either directly, or indirectly from the class Throwable. The Throwable class has two subclasses: 1. Error: An Error indicates that a non-recoverable error has occurred, that should not be caught. Errors usually cause the Java interpreter to display a message and exit. 2. Exception: An Exception indicates an abnormal condition, that must be properly handled to prevent program termination. All exceptions other than those in the RuntimeException class must be either caught or declared. Exceptions can occur for many reasons, for example, dividing a number by zero; trying to access an array element which doesn't exist. All errors and exceptions may have a message associated with them, which can be accessed using the getMessage() method. You can use this method to display a message, describing the error or exception. Here is the general syntax of exception handling in Java: try { //Code which might cause an exception } catch(Exception e) { //Exception handling code } What happens when an exception occurs in Java ? When an exception occurs in Java, an Object is created, which is of the Exception type, this is then thrown, until it is caught. If an exception occurs in a Java program and is left unhandled, the program will stop executing and the user will see a runtime error. The following code generates such a runtime error by attempting to access an array element, which doesn't exist. class exceptionExample { public static void main(String[] args) { int array[] = new int[9]; int index = 10; array[index] = 3; //illegal, since array has 10 elements } } |
Course Content > Session 10 >