Jyotisolanki: Created page with " {| border=1 | Time | Narration |- | 00:01 | Welcome to the spoken tutorial on''' Exception Handling.''' |- | 00:06 |In this tutorial we w..."

2017-09-14T07:14:16Z

Created page with " {| border=1 | <center>Time</center> | <center>Narration</center> |- | 00:01 | Welcome to the spoken tutorial on''' Exception Handling.''' |- | 00:06 |In this tutorial we w..."

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{| border=1
| <center>Time</center>
| <center>Narration</center>

|-
| 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.

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| 01:57
| Now type the following code.

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| 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'''.

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| 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.

|}

Java/C3/Exception-Handling/English-timed - Revision history

Jyotisolanki: Created page with " {| border=1 | Time | Narration |- | 00:01 | Welcome to the spoken tutorial on''' Exception Handling.''' |- | 00:06 |In this tutorial we w..."