Java – Exception Handling

February 8, 2017 SJ Exception Handling 1

In this article, we will discuss exception handling in Java in detail with examples

1. Exception:

  • An event which disrupts normal execution of a program is known as exception

2. Exception handling:

  • When such event occurs during execution of the program, in Java terms it is called as exception thrown or exception raised at runtime
  • Which results in abrupt or abnormal termination of the program and rest of the program (code i.e.; after the line where exception is raised) won’t be executed
  • To avoid abnormal termination of the program, all possible exceptions that could be thrown/raised needs to be handled
  • This is known as exception handling in Java
  • This helps to maintain graceful termination of the program

3. Alternative definition for Exception Handling:

  • Defining alternative solution or ways to maintain normalcy of the program for its graceful termination
  • Handling an unexpected event which results due to programmatic error or non-availability of required resources during run-time
  • Note: exception handling doesn’t mean that programmer correcting those raised exception, rather providing alternative way to continue with the rest of the program/code for its normal termination (graceful termination)

Q) How to handle exception in Java ?

  • The next obvious question is that, how to handle the exception raised or exception thrown
  • One way to handle exception in Java is, provide try-catch blocks
  • We will discuss and study try-catch blocks  in detail in subsequent articles
  • For time being, understand try-catch blocks or clause can be used to handle exception thrown/raised during program execution at runtime

Pseudo code for exception handling:

try {

	// program code that
	// could raise or throw exception
}
catch(ExceptionType var) {

	// handle exception here
	// provide alternative solution or way
}

4. Examples on Exception handling:

4.1 When Arithmetic exception is raised

  • In this example, arithmetic exception is thrown during execution/runtime as we are performing division by zero
  • So, any exception raised in the try-block will be caught in the catch-block and respective actions can be taken from this block like providing handling code
try {

	// divide by Zero
	int result = 19/0;
}
catch(ArithmeticException aex) {

	// exception handling code
	System.out.println("Exception handling code");
}

4.2 When null pointer exception is raised

  • In this example, null pointer exception is thrown during runtime as we are counting/checking length on a null string
  • So, any exception raised in the try-block will be caught in the catch-block and respective actions can be taken like alerting the users to enter valid string
  • Note: null string & empty string are different, as invoking length() method on empty string returns length as ZERO (0) whereas on null string it raises exception as explained above
try {

	// checking length on NULL String
	String str = null;
	int lenghtOfString = str.length();
}
catch(NullPointerException npex) {

	// exception handling code
	System.out.println("Alert !! enter valid String");
}

4.3 When Array Index out of Bounds exception is raised

  • In this example, Array Index Out of Bounds exception is thrown during execution/runtime as we are trying to assign a character at 7th position whereas its declared size is 4
  • So, any exception raised in the try-block will be caught in the catch-block and respective actions can be taken like alerting users by printing simple message like Invalid assignment
try {

	// trying to assign a character at 7th place for a char[] of 4
	char[] ch = new char[4];
	ch[7] = 'B';
}
catch(ArrayIndexOutOfBoundsException aioobex) {

	// exception handling code
	System.out.println("Invalid assignment");
}

In next article, we will see what internally happens when exception is raised during runtime without any handling code for abnormal termination

Related Articles:

References:

Happy Coding !!
Happy Learning !!

Java - Runtime mechanism, what happens when exception is thrown ?

Related posts:

  1. Java – Exception Hierarchy
  2. Java – return statement with finally block
  3. Java – User-defined Exception or Custom Exception
  4. Java – Difference between throws-clause and try-catch-finally blocks ?