Difference between revisions of "Java/C2/Using-this-keyword/English-timed"

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|-
 
|-
 
| 00:07  
 
| 00:07  
−
|  In this tutorial we will learn  
+
|  In this tutorial, we will learn:
  
 
|-
 
|-
 
| 00:09
 
| 00:09
−
| About use of '''this''' keyword  
+
|* About use of '''this''' keyword  
  
 
|-
 
|-
 
| 00:11
 
| 00:11
−
| To use '''this''' keyword with '''fields'''
+
|* To use '''this''' keyword with '''fields'''
  
 
|-
 
|-
 
| 00:14
 
| 00:14
−
| To use '''this''' keyword for chaining of constructors.  
+
|* To use '''this''' keyword for chaining of '''constructors'''.  
  
 
|-
 
|-
 
| 00:17
 
| 00:17
−
|   Here we are using
+
| Here we are using:
−
 
+
 
*Ubuntu version 11.10
 
*Ubuntu version 11.10
 
*jdk 1.6
 
*jdk 1.6
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|-
 
|-
 
|  00:28
 
|  00:28
−
| To follow this tutorial you must know  
+
| To follow this tutorial, you must know  
  
 
|-
 
|-
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|-
 
|-
 
| 00:34
 
| 00:34
−
|  If not, for relevant tutorials please visit our website which is as shown,
+
|  If not, for relevant tutorials, please visit our website which is as shown.
−
 
+
http://www.spoken-tutorial.org  
−
'''(http://www.spoken-tutorial.org)'''
+
 
|-
 
|-
 
| 00:40
 
| 00:40
−
|Now we will see the use of this key word
+
|Now we will see the use of '''this''' key word
  
 
|-
 
|-
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|-
 
|-
 
|  01:10
 
|  01:10
−
|  For that let us open '''Eclipse'''.  
+
|  For that, let us open '''Eclipse'''.  
  
 
|-
 
|-
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|-
 
|-
 
| 01:23
 
| 01:23
−
|  Comment the '''default constructor''' comment the '''constructor''' with 1 parameter.  
+
|  Comment the '''default constructor''', comment the '''constructor''' with 1 parameter.  
  
 
|-
 
|-
Line 85: Line 83:
 
|-
 
|-
 
| 02:03
 
| 02:03
−
|  Now, notice the '''parameterized constructor'''.
+
|  Now, notice the '''parametrized constructor'''.
  
 
|-
 
|-
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|-
 
|-
 
| 02:20
 
| 02:20
−
|  '''roll_number''' and '''name''' are the instance variables.  
+
|  '''roll_number''' and '''name''' are the '''instance''' variables.  
  
 
|-
 
|-
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|-
 
|-
 
| 02:55
 
| 02:55
−
|Now Save and run the file.So pressCtrl ,Sand Ctrl, F11
+
|Now '''Save''' and '''run''' the file. So press '''Ctrl, S''' and '''Ctrl, F11'''.
  
 
|-
 
|-
Line 117: Line 115:
 
|-
 
|-
 
| 03:07
 
| 03:07
−
| ''' I am a Parameterized Constructor
+
| ''' I am a Parametrized Constructor
−
 
+
 
0
 
0
−
 
 
null'''
 
null'''
  
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|-
 
|-
 
| 03:33
 
| 03:33
−
|  This is because in the '''constructor roll_number and name''' are '''local variables'''.  
+
|  This is because, in the '''constructor''', '''roll_number''' and '''name''' are '''local variables'''.  
  
 
|-
 
|-
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|-
 
|-
 
| 03:47
 
| 03:47
−
|  Here, '''roll_number''' and '''name''' will be initialized to 11 and Raju.  
+
|  Here, '''roll_number''' and '''name''' will be initialized to 11 and "Raju".  
 
|-
 
|-
 
| 03:54
 
| 03:54
−
| Because we have passed the values '''11''' and '''Raju''' the constructor.  
+
| Because we have passed the values '''11''' and '''Raju''' into the constructor.  
  
 
|-
 
|-
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|-
 
|-
 
| 04:06
 
| 04:06
−
| Then the only '''roll_number''' and '''name''' we know are the instance variables.  
+
| Then the only '''roll_number''' and '''name''' we know, are the instance variables.  
  
 
|-
 
|-
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|-
 
|-
 
| 04:21
 
| 04:21
−
|  Now, let us make a small change inside the constructor.  
+
|  Now, let us make a small change inside the '''constructor'''.  
  
 
|-
 
|-
 
| 04:29
 
| 04:29
−
| So type '''this dot roll_number equal to roll_number'''.  
+
| So, type: '''this''' dot '''roll_number''' equal to '''roll_number'''.  
  
 
|-
 
|-
 
| 04:37
 
| 04:37
−
|  And '''this dot name equal to name'''.  
+
|  And, '''this''' dot '''name''' equal to '''name'''.  
 
|-
 
|-
 
| 04:44
 
| 04:44
−
|  Now save and run the file. So press ctrl, S And Ctrl, F11 keys  
+
|  Now '''save''' and '''run''' the file. So press '''ctrl, S''' And '''Ctrl, F11''' keys.
  
 
|-
 
|-
 
| 04:51
 
| 04:51
−
| We get the output as  
+
| We get the output as:
  
 
|-
 
|-
 
| 04:53
 
| 04:53
 
|   
 
|   
−
'''I am Parameterized Constructor'''
+
'''I am Parametrized Constructor'''
−
 
+
 
'''11''' and
 
'''11''' and
−
 
 
'''Raju'''
 
'''Raju'''
  
 
|-  
 
|-  
 
| 04:58
 
| 04:58
−
|  This is because this dot roll_number and this dot name refers to the instance variables '''roll_number''' and '''name'''.
+
|  This is because '''this''' dot '''roll_number''' and '''this''' dot '''name''' refer to the instance variables '''roll_number''' and '''name'''.
  
 
|-
 
|-
 
| 05:12
 
| 05:12
−
|And here '''roll_number''' and '''name''' are the arguments passed in the method.  
+
|And here '''roll_number''' and '''name''' are the arguments, passed in the '''method'''.  
  
 
|-
 
|-
 
| 05:19
 
| 05:19
−
|  To avoid confliction between local and instance variables we use this keyword.  
+
|  To avoid conflict between '''local''' and '''instance''' variables we use this keyword.  
  
 
|-
 
|-
 
| 05:29
 
| 05:29
−
|  Now we will see the use of this keywords for chaining of '''constructor'''.  
+
|  Now we will see the use of this keyword for chaining of '''constructor'''.  
  
 
|-
 
|-
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|-
 
|-
 
| 05:43
 
| 05:43
−
|   This is called '''explicit constructor invocation'''.   
+
| This is called '''explicit constructor invocation'''.   
 
|-
 
|-
 
| 05:46
 
| 05:46
  
−
| So let us come back to the '''Student''' class which we created.  
+
| So, let us come back to the '''Student''' class which we created.  
  
 
|-
 
|-
 
|  05:53
 
|  05:53
−
|Now Remove the comments.  
+
|Now remove the comments.  
  
 
|-
 
|-
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|-
 
|-
 
| 06:52
 
| 06:52
−
|Then Comment the part which creates the second and third objects.
+
|Then '''comment''' the part which creates the second and third objects.
  
 
|-
 
|-
 
|  07:08
 
|  07:08
−
| Now let us first come to the '''constructor''' with no parameters.  
+
| Now, let us first come to the '''constructor''' with no parameters.  
  
 
|-
 
|-
 
| 07:16
 
| 07:16
−
|  After curly brackets type this within brackets '''11''' and '''semicolon'''.  
+
|  After curly brackets type: '''this''' within brackets '''11''' and semicolon.  
 
|-
 
|-
 
|  07:28
 
|  07:28
−
| Inside the second constructor type this within brackets 11 comma within double quotes Raju semicolon.  
+
| Inside the second constructor, type: '''this''' within brackets '''11''' comma within double quotes '''Raju''' semicolon.  
 
   
 
   
 
|-
 
|-
 
| 07:42
 
| 07:42
−
| Now Save and Run the file. So press Ctrl,S and Ctrl , F11.  
+
| Now, '''Save''' and '''Run''' the file. So, press '''Ctrl, S''' and '''Ctrl , F11'''.  
  
 
|-
 
|-
 
| 07:49
 
| 07:49
−
|  We get the output as   
+
|  We get the output as:  
  
 
|-
 
|-
 
| 07:51
 
| 07:51
−
|   '''I am a Parameterized Constructor'''
+
| '''I am a Parametrized Constructor'''
  
 
|-
 
|-
 
| 07:54
 
| 07:54
−
|   '''I am a constructor with a single parameter'''
+
| '''I am a constructor with a single parameter'''
  
 
|-
 
|-
 
| 07:57
 
| 07:57
−
|   '''I am Default Constructor'''
+
| '''I am Default Constructor'''
  
 
'''11''' and  
 
'''11''' and  
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|-
 
|-
 
|  08:02
 
|  08:02
−
| Now, I will explain the output.  
+
| Now, I will explain the output.  
  
 
|-
 
|-
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|-
 
|-
 
| 08:13
 
| 08:13
−
|  The constructor here is the '''no argument constructor'''.
+
|  The constructor here is the ''no argument'' '''constructor'''.
  
 
|-
 
|-
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|-
 
|-
 
| 08:24
 
| 08:24
−
| It encounters the this within brackets 11 statement.  
+
| It encounters the '''this''' within brackets '''11''' statement.  
  
 
|-
 
|-
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|-
 
|-
 
| 08:36
 
| 08:36
−
|  Then the control comes to this within brackets '''11 comma Raju'''.
+
|  Then the control comes to '''this''' within brackets '''11''' comma '''Raju'''.
  
 
|-
 
|-
Line 313: Line 307:
 
|-
 
|-
 
| 08:53
 
| 08:53
−
|  So this '''constructor''' is executed and we get the output as '''I am Parameterized Constructor'''.  
+
|  So, this '''constructor''' is executed and we get the output as '''I am Parametrized Constructor'''.  
  
 
|-
 
|-
 
| 09:02
 
| 09:02
−
|Now the instance variables will be initialized to '''11''' and '''Raju'''.As we have passed.  
+
|Now the instance variables will be initialized to '''11''' and '''Raju'''. As we have passed.  
  
 
|-
 
|-
 
| 09:11
 
| 09:11
−
|  Now, the control goes back to the calling constructor.  
+
|  Now, the control goes back to the calling '''constructor'''.  
  
 
|-
 
|-
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|-
 
|-
 
| 09:30
 
| 09:30
−
|  So we get output as I am a default '''constructor'''.
+
|  So we get output as '''I am a default constructor'''.
  
 
|-
 
|-
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|-
 
|-
 
| 10:07
 
| 10:07
−
|  '''Constructor''' call must be the first statement in the '''constructor'''.
+
|  '''Constructor call must be the first statement in the constructor'''.
  
 
|-
 
|-
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|-
 
|-
 
|  10:31
 
|  10:31
−
|  So in this tutorial, we learnt  
+
|  So in this tutorial, we learnt:
  
 
|-
 
|-
 
| 10:35
 
| 10:35
−
| To use '''this''' keyword with fields.
+
|* To use '''this''' keyword with '''field'''s.
  
 
|-
 
|-
 
| 10:38
 
| 10:38
−
| To use '''this''' keyword for chaining '''constructors'''
+
|* To use '''this''' keyword for chaining '''constructors'''
  
 
|-
 
|-
Line 421: Line 415:
 
|-
 
|-
 
|  11:07
 
|  11:07
−
|  To know more about the Spoken Tutorial Project
+
|  To know more about the Spoken Tutorial project,
  
 
|-
 
|-
 
| 11:09
 
| 11:09
−
|  Watch the video available at the following link [http://spoken-tutorial.org/What_is_a_Spoken_Tutorial http://spoken-][http://spoken-tutorial.org/What_is_a_Spoken_Tutorial tutorial.org/What_is_a_Spoken_Tutorial]  
+
|  watch the video available at the following link [http://spoken-tutorial.org/What_is_a_Spoken_Tutorial]
  
 
|-
 
|-
 
| 11:12
 
| 11:12
−
|  It summarizes the Spoken Tutorial project  
+
|  It summarizes the Spoken Tutorial project.
 
|-
 
|-
 
| 11:16
 
| 11:16
−
|  If you do not have good bandwidth, you can download and watch it  
+
|  If you do not have good bandwidth, you can download and watch it.
  
 
|-
 
|-
 
|  11:19  
 
|  11:19  
−
|  The Spoken Tutorial Project Team
+
|  The Spoken Tutorial project team:
 
|-
 
|-
 
| 11:23
 
| 11:23
−
|  Conducts workshops using spoken tutorials  
+
|  Conducts workshops using spoken tutorials.
  
 
|-
 
|-
 
| 11:26
 
| 11:26
−
| Gives certificates for those who pass an online test  
+
| Gives certificates for those who pass an online test.
  
 
|-
 
|-
 
| 11:30
 
| 11:30
−
|  For more details, please write to contact@spoken-tutorial.org  
+
|  For more details, please write to contact@spoken-tutorial.org.
 
|-
 
|-
 
|  11:36
 
|  11:36
−
|  Spoken Tutorial Project is a part of the Talk to a Teacher project  
+
|  Spoken Tutorial Project is a part of the Talk to a Teacher project.
  
 
|-
 
|-
 
| 11:40
 
| 11:40
−
|  It is supported by the National Mission on Education through ICT, MHRD, Government of India  
+
|  It is supported by the National Mission on Education through ICT, MHRD, Government of India.
 
|-
 
|-
 
| 11:46
 
| 11:46
−
|  More information on this Mission is available at  http://spoken-tutorial.org/NMEICT-Intro
+
|  More information on this mission is available at  http://spoken-tutorial.org/NMEICT-Intro.
  
 
|-
 
|-
Line 465: Line 459:
 
|-
 
|-
 
| 11:58
 
| 11:58
−
|  This is Arya Ratish signing off. Thanks for joining.
+
|  This is Arya Ratish, signing off. Thanks for joining.

Revision as of 12:19, 1 April 2015

Time Narration
00:02 Welcome to the Spoken Tutorial on using this keyword in java.
00:07 In this tutorial, we will learn:
00:09 * About use of this keyword
00:11 * To use this keyword with fields
00:14 * To use this keyword for chaining of constructors.
00:17 Here we are using:
  • Ubuntu version 11.10
  • jdk 1.6
  • Eclipse 3.7.0
00:28 To follow this tutorial, you must know
00:30 how to create a constructor in java using eclipse.
00:34 If not, for relevant tutorials, please visit our website which is as shown.

http://www.spoken-tutorial.org

00:40 Now we will see the use of this key word
00:44 Within a constructor, this is a reference to the current object.
00:48 We can refer any member of the current object within a constructor using this.
00:55 Now we will see the use of this keyword with fields.
01:00 this keyword helps us to avoid name conflicts.
01:07 We can see such an example here.
01:10 For that, let us open Eclipse.
01:17 Open the Student class we had created in the earlier tutorial.
01:23 Comment the default constructor, comment the constructor with 1 parameter.
01:40 Also comment the code for creating the first two objects.
02:03 Now, notice the parametrized constructor.
02:11 the_roll_number and the_name are the arguments passed to the constructor.
02:20 roll_number and name are the instance variables.
02:26 Now, let me change the arguments to roll_number and name itself.
02:39 So inside the constructor we have:
02:42 roll_number equal to roll_number and name equal to name.
02:55 Now Save and run the file. So press Ctrl, S and Ctrl, F11.
03:04 We get the output as follows:
03:07 I am a Parametrized Constructor

0 null

03:12 Now come back to the code.
03:17 We see 2 warnings in the code.
03:20 Hover your mouse over the warning symbol.
03:23 We can see The assignment to the variable roll_number has no effect.

03:29 And The assignment to the variable name has no effect.
03:33 This is because, in the constructor, roll_number and name are local variables.
03:40 Local variables are variables that are accessible within the method or block.
03:47 Here, roll_number and name will be initialized to 11 and "Raju".
03:54 Because we have passed the values 11 and Raju into the constructor.
04:01 But once they come out of the constructor, it is not accessible.
04:06 Then the only roll_number and name we know, are the instance variables.
04:13 They have been initialized to 0 and null already once the object is created.
04:18 So we got the output as 0 and null.
04:21 Now, let us make a small change inside the constructor.
04:29 So, type: this dot roll_number equal to roll_number.
04:37 And, this dot name equal to name.
04:44 Now save and run the file. So press ctrl, S And Ctrl, F11 keys.
04:51 We get the output as:
04:53

I am Parametrized Constructor 11 and Raju

04:58 This is because this dot roll_number and this dot name refer to the instance variables roll_number and name.
05:12 And here roll_number and name are the arguments, passed in the method.
05:19 To avoid conflict between local and instance variables we use this keyword.
05:29 Now we will see the use of this keyword for chaining of constructor.
05:34 We can use this keyword inside a constructor to call another one.
05:39 The constructors must be in the same class.
05:43 This is called explicit constructor invocation.
05:46 So, let us come back to the Student class which we created.
05:53 Now remove the comments.
06:28 Now comment the part to assign the instance variables to their values in the first two constructors.
06:52 Then comment the part which creates the second and third objects.
07:08 Now, let us first come to the constructor with no parameters.
07:16 After curly brackets type: this within brackets 11 and semicolon.
07:28 Inside the second constructor, type: this within brackets 11 comma within double quotes Raju semicolon.
07:42 Now, Save and Run the file. So, press Ctrl, S and Ctrl , F11.
07:49 We get the output as:
07:51 I am a Parametrized Constructor
07:54 I am a constructor with a single parameter
07:57 I am Default Constructor

11 and

Raju

08:02 Now, I will explain the output.
08:08 When the object is created, the respective constructor gets called.
08:13 The constructor here is the no argument constructor.
08:20 The control comes to the first line in the constructor.
08:24 It encounters the this within brackets 11 statement.
08:26 Hence it calls the constructor that accepts single integer argument.
08:36 Then the control comes to this within brackets 11 comma Raju.
08:44 Hence it calls the constructor that accepts 1 integer and 1 String argument.
08:53 So, this constructor is executed and we get the output as I am Parametrized Constructor.
09:02 Now the instance variables will be initialized to 11 and Raju. As we have passed.
09:11 Now, the control goes back to the calling constructor.
09:16 So the second constructor gets executed.
09:19 We get the output as I am constructor with a single parameter.
09:25 Then, the control goes to the first constructor and executes it.
09:30 So we get output as I am a default constructor.
09:36 Then studentDetail method is executed.
09:42 So, we get 11 and Raju.
09:45 Now, let us make a small change.
09:47 Make the this statement the last one in the constructor.
10:00 We get a compiler error.
10:03 Hover the mouse over the error symbol.
10:06 We get the error as:
10:07 Constructor call must be the first statement in the constructor.
10:12 So we must make it the first line of the constructor.
10:16 So make it the first line of the constructor.
10:27 Now we can see that the error has gone.
10:31 So in this tutorial, we learnt:
10:35 * To use this keyword with fields.
10:38 * To use this keyword for chaining constructors
10:41 How this keyword should be used within a constructor.
10:45 For self assessment, in the Employee class created earlier:
10:49 Create a constructor with two parameters
10:52 Use this keyword to initialize the instance variables .
10:57 Also create a constructor with 1 and no parameters.
11:01 Try chaining the constructors using this as explained in the tutorial.
11:07 To know more about the Spoken Tutorial project,
11:09 watch the video available at the following link [1]
11:12 It summarizes the Spoken Tutorial project.
11:16 If you do not have good bandwidth, you can download and watch it.
11:19 The Spoken Tutorial project team:
11:23 Conducts workshops using spoken tutorials.
11:26 Gives certificates for those who pass an online test.
11:30 For more details, please write to contact@spoken-tutorial.org.
11:36 Spoken Tutorial Project is a part of the Talk to a Teacher project.
11:40 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
11:46 More information on this mission is available at http://spoken-tutorial.org/NMEICT-Intro.
11:55 Thus We have come to the end of this tutorial.
11:58 This is Arya Ratish, signing off. Thanks for joining.

Contributors and Content Editors

Arya Ratish, Gaurav, Kaushik Datta, PoojaMoolya, Sandhya.np14, Sneha

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