Difference between revisions of "Java/C2/Instance-fields/English-timed"

Revision as of 16:12, 30 March 2015

Time	Narration
00:02	Welcome to the Spoken Tutorial on Instance fields in Java.
00:06	In this tutorial, we will learn
00:08	About instance fields
00:10	To access the instance fields of a class
00:13	Modifiers for instance fields
00:15	And Why instance fields are called so?
00:18	Here we are using
00:20	Ubuntu version 11.10
00:22	jdk 1.6
00:24	And Eclipse IDE 3.7.0
00:27	To follow this tutorial you must know
00:30	how to create a class in Java using Eclipse.
00:33	You must also know how to create an object for the class.
00:38	If not, for relevant tutorials please visit our website which is as shown, (http://www.spoken-tutorial.org)
00:43	We know that objects store their individual states in fields.
00:48	These fields are declared without the static keyword.
00:51	We will learn about static fields in the coming tutorials.
00:55	Non-static fields are also known as instance variables or instance fields.
01:01	Let us go back to the Student class we had already created.
01:09	We can see that here roll_no and name are the instance fields of this class.
01:15	Now, we will learn how to access these fields.
01:18	For that, let us open the TestStudent class which we had already created.
01:27	We can remove the statement for creating the second object.
01:33	We will also remove the println statements.
01:41	Now we will access the fields roll_no and name of the student class usingstud1 and the dot operator.
01:49	So for that type System' dot out dot println within brackets and double quotes, The roll number is, then plus stud1 dot from the option provided select roll_no press Enter then semicolon.
02:15	Next line type System dot out dot println within brackets and double quotes The name is, plus stud1 dot select name press enter then semicolon.
02:39	Now, save and run the file TestStudent.java. So press Ctrl, S and Ctrl, F11.
02:48	We get the output as
02:51	The roll number is 0.
02:53	The name is null.
03:00	This is because, we have not initialized the variables to any value.
03:05	In Java, the fields cannot have random values.
03:09	After the memory is allocated for the object the fields are initialized to null or zero.
03:15	This work is done by the constructor.
03:18	We will learn about constructor in the coming tutorials.
03:21	Now, we will initialize the fields explicitly and see the output.
03:27	So type,int roll_no equal to 50 next line string name equal to within double quotes Raju.
03:42	Now, save and run the file. Press Ctrl,S and Ctrl F11
03:50	We get the output as expected The roll number is 50.
03:54	The name is Raju.
03:56	This is because we have explicitly initialize the variables in the Student class
04:04	We can see that here the fields have no modifier or the default modifier.
04:10	Recall modifiers we had discussed in Creating Classes.
04:14	We can access the fields because both Student.java and TestStudent.java are in the same package.
04:22	We can see that here they are in the same default package.
04:30	We will learn about packages in the later tutorials.
04:34	We will now change the modifier to private.
04:37	So before the field declarations type private. So type private int roll no=50.
04:48	Next line private string name =Raju.
04:53	Now save the file Student.java.
05:00	We can see that we get errors in TestStudent.java.
05:05	Hover the mouse over the error symbol.
05:08	It says The field Student dot roll number is not visible.
05:12	And The field Student dot name is not visible.
05:16	This is because private fields can be accessed only within its own class.
05:23	You can try accessing roll_no and name from the Student class itself.
05:27	You will find that you can access them without any error.
05:32	Now let us change the modifier to protected.
05:52	Now Save the file and Run the program
06:00	We see the output on the console. The Roll no is 50 the name is Raju.
06:07	This is because protected fields can be accessed within the same package.
06:17	Now let us see why instance fields are called so?
06:22	Instance fields are called so because their values are unique to each instance of a class.
06:29	In other words each object of a class will have unique values.
06:34	Let us go to the TestStudent class.
06:43	Here, we will create one more object of the Student class.
06:50	So type next lineStudent space stud2 equal to new space Student , opening and closing brackets semicolon.
07:06	We will now initialize both the objects in theTestStudent class.
07:18	Next line type stud1 dot selectroll_no press enter equal to 20 semicolon.
07:32	Next line type stud1 dot select name press enter equal to within double quotes Ramu semicolon press enter.
07:54	Thus we have initialized the fields for the first object.
07:58	Now, we will initialize the fields for the second object.
08:02	So type stud2 dot selectroll_no equal to 30 semicolon.
08:15	Next line stud2 dot select name equal to within double quotes Shyamu semicolon press enter.
08:34	Now after the println statements, type System dot out dot println within brackets and double quotes The roll number is, plus stud2 dot select roll_no and semicolon.
09:03	System dot out dot println within brackets and double quotes The name is, plus stud2 dot select name and semicolon.
09:28	Now, save and run the file. Press Ctrl,s and Ctrl, F11
09:38	We get the output as follows. The roll_no is 20, The name is' Ramu roll_no is 30, name is shyamu.
09:47	Here both stud1 and stud2 are referring to two different objects.
09:52	This means that the two objects have unique values.
09:56	We can see that here.
09:57	The first object has the values 20 and Ramu.
10:02	The second object has the values 30 and Shyamu .
10:09	Now, let us create one more object.
10:13	So type Student space stud3 equal to new space Student within brackets opening and closing brackets semicolon.
10:36	We will now, print the values of the third object
10:44	So type System dot out dot println within brackets and double quotes The roll_no is, plus stud3 dot select roll_no semicolon.
11:09	next line type System dot out dot println within brackets and double quotes The name is, plus stud3 dot name semicolon.
11:29	Now, save and run the file. So press Ctrl, S and Ctrl, F11 .
11:36	We can see that the third object contains the values 50 and Raju.
11:46	This is because we had explicitly initialized the fields of the Student class to 50 and Raju.
11:54	Now, try de-initializing the fields and see the output for the third object.
12:02	So in this tutorial, we learnt:
12:05	* About instance fields.
12:07	* Accessing the fields using dot operator.
12:11	For self assessment,
12:13	Create an object emp2 in the Test Employee class already created.
12:18	Then initialize the values of the two objects using dot operator.
12:23	Use 55 and Priya as values for first object.
12:27	Use 45 and Sandeep as values for second object.
12:31	Display values for both the objects in the output.
12:34	To know more about the Spoken Tutorial Project,
12:37	watch the video available at [1]
12:40	It summarizes the Spoken Tutorial project.
12:43	If you do not have good bandwidth, you can download and watch it.
12:47	The Spoken Tutorial project team:
12:49	Conducts workshops using spoken tutorials.
12:52	Gives certificates for those who pass an online test.
12:56	For more details, please write to contact@spoken-tutorial.org
13:01	Spoken Tutorial Project is a part of the Talk to a Teacher project.
13:05	It is supported by the National Mission on Education through ICT, MHRD, Government of India.
13:11	More information on this mission is available at [2]
13:09	Thus we have come to the end of this tutorial.
13:22	This is Arya Ratish from IIT Bombay, signing off. Thanks for joining.

Contributors and Content Editors

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

Difference between revisions of "Java/C2/Instance-fields/English-timed"

Revision as of 16:12, 30 March 2015

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@@ Line 5: / Line 5: @@
 |-
 |  00:02
-|  Welcome to the Spoken Tutorial on '''Instance Fields''' in '''Java'''.
+| Welcome to the Spoken Tutorial on '''Instance fields''' in '''Java'''.
 |-
 | 00:06
-| In this tutorial we will learn
+| In this tutorial, we will learn
 |-
@@ Line 25: / Line 25: @@
 | 00:15
 | And Why '''instance fields''' are called so?
 |-
@@ Line 42: / Line 39: @@
 | 00:24
 |  And  Eclipse IDE 3.7.0
 |-
@@ Line 52: / Line 47: @@
 | 00:30
 |  how to create a '''class '''in '''Java '''using '''Eclipse'''.
 |-
 | 00:33
 |  You must also know how to create an '''object '''for the '''class'''.
 |-
@@ Line 68: / Line 61: @@
 | 00:43
 |  We know that objects store their individual states in''' fields'''.
 |-
 | 00:48
 |  These fields are declared without the  '''static'''  keyword.
 |-
 | 00:51
 |  We will learn about''' static fields''' in the coming tutorials.
 |-
 | 00:55
 |  '''Non-static fields''' are also known as '''''instance variables '''''or''''' instance fields.'''''
 |-
 |  01:01
 |   Let us go back to the '''Student class''' we had already created.
 |-
 | 01:09
 |  We can see that here''' roll_no''' and '''name''' are the '''instance fields''' of this '''class'''.
 |-
@@ Line 104: / Line 89: @@
 |  01:18
 |  For that, let us open the '''TestStudent class '''which we had already created.
 |-
 | 01:27
 |  We can remove the statement for creating the second '''object'''.
 |-
 | 01:33
 |  We will also remove the '''println '''statements.
 |-
 | 01:41
 |  Now we will access the fields '''roll_no''' and '''name'''  of the student class using'''stud1 '''and the''' dot operator'''.
 |-
 | 01:49
 |  So for that  type '''System''' ''dot'' '''out''' ''dot'' '''println''' within brackets and double quotes, '''The roll number is''', then ''plus '''''stud1''''' dot ''''' from the option provided select''''' roll_no''''' '' press '''Enter'''  then ''semicolon''.
 |-
 | 02:15
 |  Next line type '''System''' ''dot'' '''out''' ''dot'' '''println''' within brackets and double quotes '''The name is''',   ''plus '''''stud1''''' dot select  '''''name'''''   press '''enter''' ''  then ''semicolon''.
 |-
@@ Line 138: / Line 117: @@
 | 02:48
 |   We get the output as
 |-
@@ Line 151: / Line 129: @@
 |03:00
 |   This is because, we have not initialized the '''variables''' to any value.
 |-
 | 03:05
 |  In '''Java''', the '''fields''' cannot have random values.
 |-
 | 03:09
 |  After the '''memory''' is allocated for the '''object''' the '''fields''' are initialized to '''null '''or '''zero'''.
 |-
 | 03:15
 |  This work is done by the '''constructor'''.
 |-
@@ Line 175: / Line 149: @@
 | 03:21
 |  Now, we will initialize the '''fields''' explicitly and see the '''output'''.
 |-
@@ Line 184: / Line 157: @@
 | 03:42
 | | Now, '''save '''and '''run '''the file. Press '''Ctrl,S''' and '''Ctrl F11 '''
 |-
 | 03:50
 |  We get the '''output''' as expected '''The roll number is 50'''.
 |-
@@ Line 198: / Line 169: @@
 |  03:56
 |This is because we have explicitly initialize the variables  in the '''Student''' class
 |-
 | 04:04
 |  We can see that here the '''fields '''have no '''modifier '''or''' '''the''' default modifier'''.
 |-
 | 04:10
 |  Recall '''modifiers''' we had discussed in '''Creating Classes.'''
 |-
 | 04:14
 |  We can access the fields because both '''Student.java''' and '''TestStudent.java''' are in the same '''package'''.
 |-
 | 04:22
 |  We can see that here they are in the same '''default package'''.
 |-
@@ Line 228: / Line 193: @@
 | 04:34
 | We will now change the modifier to '''private'''.
 |-
 | 04:37
 |  So before the '''field''' declarations type '''private'''. So type '''private int ''' '''roll no=50'''.
 |-
@@ Line 246: / Line 209: @@
 |  05:00
 | | We can see that we get errors in '''TestStudent.java'''.
 |-
 | 05:05
 |  Hover the mouse over the error symbol.
 |-
@@ Line 261: / Line 222: @@
 | 05:12
 | And '''The field Student '''''dot '''''name '''is not visible.
 |-
 | 05:16
 |  This is because private fields can be accessed only within its own class.
 |-
 | 05:23
 |  You can try accessing '''roll_no''' and '''name''' from the '''Student class '''itself.
 |-
 | 05:27
 |  You will find that you can access them without any error.
 |-
@@ Line 302: / Line 258: @@
 | 06:22
 |  '''Instance fields''' are called so because their values are unique to each '''''instance''''' of a class.
 |-
@@ Line 311: / Line 266: @@
 |  06:34
 |  Let us go to the '''TestStudent class'''.
 |-
 | 06:43
 |  Here, we will create one more object of the '''Student class'''.
 |-
@@ Line 325: / Line 278: @@
 | 07:06
 |  We will now initialize both the objects in the'''TestStudent class'''.
 |-
 | 07:18
 |  Next line type '''stud1''' ''dot '' select'''roll_no'''  press ''' enter''' equal to '''20 '''  ''semicolon.''
 |-
 | 07:32
 |  Next line type '''stud1''' ''dot'' select  '''name''' press '''enter''' equal to within double quotes '''Ramu '''''semicolon'' press '''enter'''.
 |-
 | 07:54
 |  Thus we have initialized the fields for the first object.
 |-
 | 07:58
 |  Now, we will initialize the fields for the second object.
 |-
 | 08:02
 |  So type '''stud2''' ''dot'' select'''roll_no''' equal to '''30 '''  ''semicolon''.
 |-
 |08:15
 | Next line   '''stud2''' ''dot'' select '''name''' equal to within double quotes''' Shyamu '''''semicolon'''''  press''' enter'''.
 |-
 | 08:34
 |  Now after the '''println''' statements, type '''System''' '''dot''' '''out''' dot '''println''' within brackets and double quotes '''The roll number is''',  ''plus '''''stud2 '''''dot  select '''''roll_no''''' ''and  ''semicolon''.
 |-
 | 09:03
 |  '''System''' ''dot'' '''out''' ''dot'' '''println''' within brackets and double quotes '''The name is''',  ''plus '''''stud2 '''''dot select '''''name''''' ''and   ''semicolon''.
 |-
@@ Line 374: / Line 318: @@
 | 09:38
 |   We get the output as follows.  The roll_no is '''20'', The name is''' Ramu''' roll_no is '''30''',   name is''' shyamu'''.
 |-
 | 09:47
 |  Here both '''stud1''' and '''stud2''' are referring to two different '''objects'''.
 |-
 | 09:52
 |  This means that the two '''objects''' have unique values.
 |-
 | 09:56
 |  We can see that here.
 |-
 | 09:57
 |  The first object has the values '''20''' and '''Ramu'''.
 |-
@@ Line 403: / Line 342: @@
 |  10:09
 |   Now, let us create one more '''object.'''
 |-
 | 10:13
 |  So type '''Student''' space '''stud3''' equal to '''new''' space '''Student'''  within brackets opening and closing brackets semicolon.
 |-
@@ Line 432: / Line 369: @@
 |  11:46
 |  This is because we had explicitly initialized the fields of the '''Student''' class to''' 50''' and ''' Raju'''.
 |-
 | 11:54
-|  Now, try de-initializing the fields and see the output for the third object.
+|  Now, try de-initializing the '''field'''s and see the output for the third object.
 |-
 |  12:02
-| So in this tutorial, we learnt
+| So in this tutorial, we learnt:
 |-
 | 12:05
-|   About instance fields.
+|* About instance fields.
 |-
 | 12:07
-|  Accessing the fields using dot operator.
+|* Accessing the fields using dot operator.
 |-
 |  12:11
 | | For self assessment,
 |-
 | 12:13
-|  Create an  object emp2 in the Test Employee class already created.
+| Create an  object '''emp2''' in the '''Test Employee''' '''class''' already created.
 |-
 | 12:18
 |  Then initialize the values of the two objects using dot operator.
 |-
 | 12:23
 |  Use 55 and Priya as values for first object.
 |-
@@ Line 477: / Line 407: @@
 |-
 | 12:31
-|  Display the values for both the objects in the output.
+|  Display values for both the objects in the output.
 |-
 |  12:34
-|  To know more about the Spoken Tutorial Project
+|  To know more about the Spoken Tutorial Project,
 |-
 | 12:37
-|   Watch the video available at [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 [http://spoken-tutorial.org/What_is_a_Spoken_Tutorial]
 |-
 | 12:40
-|   It summarizes the Spoken Tutorial project
+| It summarizes the Spoken Tutorial project.
 |-
 | 12:43
-|   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.
 |-
 |    12:47
-| The Spoken Tutorial Project Team
+| The Spoken Tutorial project team:
 |-
 |12:49
-|   Conducts workshops using spoken tutorials
+| Conducts workshops using spoken tutorials.
 |-
 |  12:52
-|  Gives certificates for those who pass an online test
+| Gives certificates for those who pass an online test.
 |-
 | 12:56
-|   For more details, please write to contact@spoken-tutorial.org
+| For more details, please write to contact@spoken-tutorial.org
 |-
 |  13:01
-|   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.
 |-
 | 13:05
-|  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.
 |-
 | 13:11
-|   More information on this Mission is available at
+|   More information on this mission is available at
-  [http://spoken-tutorial.org/NMEICT-Intro http://spoken-tutorial.org/NMEICT-Intro]
+ [http://spoken-tutorial.org/NMEICT-Intro]
 |-
@@ Line 534: / Line 459: @@
 |-
 | 13:22
-|  This is Arya Ratish from IIT Bombay signing off.   Thanks for joining.
+|  This is Arya Ratish from IIT Bombay, signing off. Thanks for joining.