Java/C3/Exception-Handling/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Exception Handling.
00:06	In this tutorial we will learn about: What is an exception Checked and unchecked exceptions Handling the exceptions using try-catch block and finally block .
00:20	Here we are using Ubuntu Linux 16.04 OS JDK 1 .8 and Eclipse 4.3.1
00:32	To follow this tutorial, you must have knowledge of basics of Java and Eclipse IDE.
00:39	If not, for relevant Java tutorials, please visit the link shown.
00:45	An exception is an unexpected event, which occurs during the execution of a program.
00:52	It interrupts the normal flow of the program and results in an abnormal termination.
01:00	Based on their occurrence, exceptions are classified as unchecked exceptions and checked exceptions.
01:08	Now we will open eclipse and create a new project called ExceptionDemo.
01:16	Inside this project we will create the necessary classes to demonstrate exception handling.
01:24	We will create a new class Marks.
01:28	Now type the following code to represent the Marks class.
01:34	This program prints the marks of 5 students that is stored in an array marks.
01:41	Let us run this program and verify the output.
01:45	We can see that the values in the array are getting printed.
01:50	Let us check what will happen if we are trying to access an array element which is not existing.
01:57	Now type the following code.
02:00	We know that there are only 5 elements in our array.
02:04	But in this statement we are trying to access the element at index 50 which is not existing.
02:12	Let us run this program now.
02:15	We can see that the program terminates with an error message:“ArrayIndexOutOfBoundsException “at line number 7.
02:25	The error message indicates the details of the exception like type of exception where it occurred and other details.
02:35	Note that the print statement is not executed as the program terminates after the error.
02:42	This is an example of Unchecked exception.
02:46	Unchecked exceptions are called as Runtime exception as it is checked only during the execution.
02:54	They handle the programming bugs and logical errors such as Dividing a number by zero and Accessing an array element which is not existing .
03:07	Now let us learn about how to handle an exception using try catch block.
03:13	This portion of the code within a try block, can possibly raise an exception.
03:19	The corresponding catch block can receive the exception details in object e.
03:26	Inside the catch block we can write the code for displaying error messages or recovering from the error.
03:34	Now let us switch to eclipse.
03:37	First let us add a try block around the code which caused the exception like this.
03:44	Now we have to add a corresponding catch block.
03:48	So type the following code.
03:51	Here we are printing a custom message “Array Overflow Exception occurred”
03:57	Inside the round brackets we have created an instance of ArrayIndexOutOfBoundsException.
04:05	So this block can catch exceptions of type ArrayIndexOutOfBoundsException.
04:11	Now let us run the program.
04:14	We can see that the error message gets printed.
04:18	But this time, note that printing the marks array is also executed.
04:24	In this way we can handle exceptions.
04:27	Next let us see how to use multiple catch blocks.
04:32	We can use them when different types of exceptions are raised by a block.
04:38	Type the following code inside the try block.
04:42	This line of code divides an array element by zero as the value of a is zero.
04:49	So an ArithmeticException will be raised first.
04:53	Let us now add one more catch block to handle the ArithmeticException.
04:58	So type the following code after the existing catch block.
05:03	Let us run the program again.
05:06	This time the error message "Arithmetic Exception occurred" gets printed as it is caught first.
05:13	The remaining portion of the code outside the try catch block executes.
05:19	Next let us see about checked exceptions.
05:23	Checked exceptions are checked at compile time.
05:27	So they must be handled before running the program.
05:31	For example: Accessing a file which is not existing or Accessing a network system when the network is down .
05:41	Now let us switch to Eclipse and create a new class MarksFile.
05:47	Let us add main method.
05:50	Now we want to read a file located in the computer.
05:54	So type the following code.
05:57	Here the FileReader object fr is initialized as null.
06:03	FileReader object can be used to access and read a particular file.
06:08	Eclipse will show an error.
06:11	To rectify the error, click on it and double click import FileReader java dot io.
06:19	The FileReader class is imported from the java dot io package.
06:25	We will learn about package and its usage in detail in a later tutorial.
06:31	To allow fr to access a file called Marks which is located in the home folder, type the following code.
06:40	The path shown here is to be replaced with that of your system's home folder.
06:46	Now an error comes up. It indicates that this line of code can create a FileNotFoundException.
06:55	Click on the error and double click Surround with try/catch.
07:00	We can see that Eclipse automatically inserts the try catch block to rectify this error.
07:08	So we can understand that this is a checked exception.
07:12	Next let us see how to use finally block.
07:16	Type the following code.
07:18	finally block usually follows a try-catch block .
07:22	The code inside this block is executed whether exception has occurred or not. It contains a print statement.
07:32	Now let us close the file reference inside the finally block.
07:37	So type, fr dot close
07:40	Now Eclipse indicates that this will raise an IOException.
07:45	So click on the error and double click Surround with try/catch.
07:51	Now let us run the program.
07:54	We can see that FileNotFoundException message is printed.
07:59	This is because we don't have a file named Marks in our home folder.
08:04	We can also see a NullPointerException as fr still refers to a null value.
08:12	But we can see that the print statement inside finally block gets executed.
08:18	Let us now create a text file Marks in our home folder.
08:23	If you are a windows user, create a text file in your local drive and mention its path.
08:29	For example it can be specified as D:\\Marks.txt
08:37	Let us now run the program again.
08:40	We can verify that there are no exceptions once the Marks file is created.
08:46	And “Inside finally block” gets printed.
08:50	The cleanup operation i.e closing the FileReader Object fr is also executed successfully.
08:58	With this we come to the end of this tutorial.
09:02	Let us summarize.
09:04	In this tutorial we have learnt about: What is an Exception Checked and Unchecked Exceptions Handling the Exceptions using the try-catch block finally block .
09:17	As an assignment, Learn about another Runtime Exception called NullPointerException.
09:24	Refer to the Java program named Demo.java provided in the Assignment link of this tutorial.
09:31	An exception will be raised when you run this code.
09:35	Identify the code which is responsible for the exception.
09:40	Rectify it using a try-catch block.
09:43	The video at the following link summarizes the Spoken Tutorial Project. Please download and watch it.
09:52	The Spoken Tutorial Project Team Conducts workshops using spoken tutorials , Gives certificates on passing the online tests.For more details, please write to us.
10:04	Spoken Tutorial Project is funded by the NMEICT, MHRD, Government of India. More information on this Mission is available at the link shown.
10:15	This script has been contributed by:Dept. of Information Technology, Amal Jyothi College of Engineering.
10:23	This is Priya from IIT Bombay. Thanks for joining.

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