Exception Handling Fundamentals:

A Java exception is an object which describes an exceptional (that is, error) condition which has occurred in a piece of code. Whenever an exceptional condition arises and an object representing that exception is created and thrown in the method which caused the error.  Those functions might select to handle the exception itself, or pass it on. Or in other hands way, at any point the exception is processed and caught. Exceptions can be produced through the Java run-time system, or they can be manually produced through your code. Exceptions thrown through Java relate to fundamental errors which violate the rules of the Java language or the constraints of the Java execution environment. Manually produce exceptions are typically used to report any error condition to the caller of a method.

Java exception handling is managed through five keywords; throw, try catch, finally and throws.  In brief here is how they work. Program statements which you need to monitor for exceptions are hold inside a try block.  If an exception occurs within the try block, it is thrown.  Your code could catch this exception (using catch) and handle it in some rational manner. A System-generated exception is automatically thrown through the Java run-time system. For manually throw an exception, use the keyword throw. Any exception which is thrown out of a method must be specified as such through a throws clause. Any code which absolutely must be executed before a method returns is put in a finally block.

This is the common form of an exception-handling block:

try{

/ / block of code to monitor for errors

}

catch (ExceptionType1 exOb){

/ / Exception Type1

}

catch (ExceptionType2 exOb) {

/ / Exception Type2

}

/ / ...

finally{

/ / block of code to be executed.

}

Here Exception type is the category of exception which has occurred. The remainder of this lesson describes how to apply this framework.