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

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|-
 
|-
 
| 00:02
 
| 00:02
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|  Welcome to the Spoken Tutorial on using this keyword in java.  
+
|  Welcome to the Spoken Tutorial on '''using this keyword''' in '''java'''.  
  
 
|-
 
|-
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|-
 
|-
 
| 00:09
 
| 00:09
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| 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.  
  
 
|-
 
|-
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|-
 
|-
 
| 00:30
 
| 00:30
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|  how to create a constructor in java using eclipse.  
+
|  how to create a '''constructor''' in '''java''' using '''eclipse'''.  
  
 
|-
 
|-
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|  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
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|-
 
|-
 
| 00:44
 
| 00:44
−
| Within a constructor, this is a reference to the current object.  
+
| Within a constructor, '''this''' is a reference to the current '''object'''.  
  
 
|-
 
|-
 
| 00:48
 
| 00:48
−
|  We can refer any member of the current object within a constructor using this.  
+
|  We can refer any member of the current '''object''' within a '''constructor''' using '''this'''.  
  
 
|-
 
|-
 
| 00:55
 
| 00:55
−
|Now we will see the use of this keyword with fields.   
+
|Now we will see the use of '''this''' keyword with fields.   
  
 
|-
 
|-
 
| 01:00
 
| 01:00
−
| this keyword helps us to avoid name conflicts.  
+
| '''this''' keyword helps us to avoid name conflicts.  
  
 
|-
 
|-
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|-
 
|-
 
|  01:10
 
|  01:10
−
|  For that let us open Eclipse.  
+
|  For that let us open '''Eclipse'''.  
  
 
|-
 
|-
 
| 01:17
 
| 01:17
−
|  Open the Student class we had created in the earlier tutorial.  
+
|  Open the '''Student class''' we had created in the earlier tutorial.  
  
 
|-
 
|-
 
| 01:23
 
| 01:23
−
|  Comment the default constructor comment the constructor with 1 parameter.  
+
|  Comment the '''default constructor''' comment the '''constructor''' with 1 parameter.  
  
 
|-
 
|-
 
| 01:40
 
| 01:40
−
|  Also comment the code for creating the first two objects.  
+
|  Also comment the code for creating the first two '''objects'''.  
  
 
|-
 
|-
 
| 02:03
 
| 02:03
−
|  Now, notice the parameterized constructor.
+
|  Now, notice the '''parameterized constructor'''.
  
 
|-
 
|-
 
| 02:11
 
| 02:11
−
| the_roll_number and the_name are the arguments passed to the constructor.  
+
| '''the_roll_number''' and '''the_name''' are the arguments passed to the constructor.  
  
 
|-
 
|-
 
| 02:20
 
| 02:20
−
|  roll_number and name are the instance variables.  
+
|  '''roll_number''' and '''name''' are the instance variables.  
  
 
|-
 
|-
 
| 02:26
 
| 02:26
−
|  Now, let me change the arguments to roll_number and name itself.  
+
|  Now, let me change the arguments to '''roll_number''' and '''name''' itself.  
  
 
|-
 
|-
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|-
 
|-
 
| 02:42
 
| 02:42
−
|  roll_number equal to roll_number and name equal to name.
+
|  '''roll_number''' equal to '''roll_number''' and '''name''' equal to '''name'''.
  
 
|-
 
|-
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|-
 
|-
 
| 03:07
 
| 03:07
−
| I am a Parameterized Constructor
+
| ''' I am a Parameterized Constructor
  
 
0
 
0
  
−
null
+
null'''
  
 
|-
 
|-
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|-
 
|-
 
| 03:23
 
| 03:23
−
|We can see The assignment to the variable roll_number has no effect.
+
|We can see '''The assignment to the variable roll_number has no effect.'''
 
'''
 
'''
 
|-
 
|-
 
| 03:29
 
| 03:29
−
| And The assignment to the variable name has no effect.
+
| And '''The assignment to the variable name has no effect'''.
  
 
|-
 
|-
 
| 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'''.  
  
 
|-
 
|-
 
| 03:40
 
| 03:40
−
|  Local variables are variables that are accessible within the method or block.  
+
|  '''Local variables''' are variables that are accessible within the method or block.  
  
 
|-
 
|-
 
| 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 Rajuthe constructor.  
+
| Because we have passed the values '''11''' and '''Raju''' 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.  
  
 
|-
 
|-
 
| 04:13
 
| 04:13
−
|  They have been initialized to 0 and null already once the object is created.  
+
|  They have been initialized to '''0''' and '''null''' already once the object is created.  
  
 
|-
 
|-
 
| 04:18
 
| 04:18
−
|  So we got the output as 0 and null.  
+
|  So we got the output as '''0''' and '''null'''.  
 
|-
 
|-
 
| 04:21
 
| 04:21
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|-
 
|-
 
| 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
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|-  
 
|-  
 
| 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 refers 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.  
  
 
|-
 
|-
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|-
 
|-
 
| 05:39
 
| 05:39
−
|  The constructors must be in the same class.
+
|  The '''constructors''' must be in the same class.
  
 
|-
 
|-
 
| 05:43
 
| 05:43
−
|    This is called explicit constructor invocation.   
+
|    This is called '''explicit constructor invocation'''.   
 
|-
 
|-
 
| 05:46
 
| 05:46
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|-
 
|-
 
|  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
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|-
 
|-
 
| 08:08
 
| 08:08
−
|  When the object is created, the respective constructor gets called.  
+
|  When the object is created, the respective '''constructor''' gets called.  
  
 
|-
 
|-
 
| 08:13
 
| 08:13
−
|  The constructor here is the no argument constructor.
+
|  The constructor here is the no argument '''constructor'''.
  
 
|-
 
|-
 
| 08:20
 
| 08:20
−
|  The control comes to the first line in the constructor.
+
|  The control comes to the first line in the '''constructor'''.
  
 
|-
 
|-
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|-
 
|-
 
| 08:26
 
| 08:26
−
|  Hence it calls the constructor that accepts single integer argument.  
+
|  Hence it calls the '''constructor''' that accepts single integer argument.  
  
 
|-
 
|-
 
| 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'''.
  
 
|-
 
|-
 
| 08:44
 
| 08:44
−
|  Hence it calls the constructor that accepts 1 integer and 1 String argument.  
+
|  Hence it calls the '''constructor''' that accepts '''1 integer''' and '''1 String''' argument.  
  
 
|-
 
|-
 
| 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 Parameterized 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.  
  
 
|-
 
|-
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|-
 
|-
 
| 09:19
 
| 09:19
−
|  We get the output as I am constructor with a single parameter.
+
|  We get the output as '''I am constructor with a single parameter'''.
  
 
|-
 
|-
 
| 09:25  
 
| 09:25  
−
|  Then, the control goes to the first constructor and executes it.  
+
|  Then, the control goes to the first '''constructor''' and executes it.  
  
 
|-
 
|-
 
| 09:30
 
| 09:30
−
|  So we get output as I am a default constructor.
+
|  So we get output as I am a default '''constructor'''.
  
 
|-
 
|-
 
| 09:36
 
| 09:36
−
|  Then studentDetail method is executed.  
+
|  Then '''studentDetail''' method is executed.  
  
 
|-
 
|-
 
| 09:42
 
| 09:42
−
|  So, we get 11 and Raju.  
+
|  So, we get '''11''' and '''Raju'''.  
  
 
|-
 
|-
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|-
 
|-
 
| 09:47
 
| 09:47
−
| Make the this statement the last one in the constructor.  
+
| Make the this statement the last one in the '''constructor'''.  
  
 
|-
 
|-
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|-
 
|-
 
|  10:12
 
|  10:12
−
|  So we must make it the first line of the constructor.
+
|  So we must make it the first line of the '''constructor'''.
  
 
|-
 
|-
 
|  10:16
 
|  10:16
−
| So make it the first line of the constructor.
+
| So make it the first line of the '''constructor'''.
  
 
|-
 
|-

Revision as of 17:37, 16 January 2014

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 parameterized 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 pressCtrl ,Sand Ctrl, F11
03:04 We get the output as follows:
03:07 I am a Parameterized 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 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 Parameterized Constructor

11 and

Raju

04:58 This is because this dot roll_number and this dot name refers 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 confliction between local and instance variables we use this keyword.
05:29 Now we will see the use of this keywords 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 Parameterized 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 Parameterized 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 http://spoken-tutorial.org/What_is_a_Spoken_Tutorial
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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