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

| 00:02

| Welcome to the Spoken Tutorial on '''Instance fields''' in '''Java'''.

| 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?

|00:22

|'''jdk 1.6'''

|00:24

|And  '''Eclipse IDE 3.7.0'''

| 00:27

| To follow this tutorial, you must know  

| how to create a '''class '''in '''Java''' using '''Eclipse'''.

| You must also know how to create an '''object '''for the '''class'''.

| If not, for relevant tutorials, please visit our website which is as shown.

http://www.spoken-tutorial.org  

| We know that objects store their individual states in''' fields'''.

| These fields are declared without the  '''static'''  keyword.

| We will learn about''' static fields''' in the coming tutorials.

| '''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.

| We can see that here''' roll_no''' and '''name''' are the '''instance fields''' of this '''class'''.

| Now, we will learn how to access these '''fields'''.

| 01:18

| For that, let us open the '''TestStudent class '''which we had already created.

| We can remove the statement for creating the second '''object'''.

| We will also remove the '''println '''statements.

| Now we will access the '''fields''', '''roll_no''' and '''name''', of the student class using '''stud1 '''and the ''dot operator''.

| 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.  

|  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.

|  We get the output as:

|  After the '''memory''' is allocated for the '''object''', the '''fields''' are initialized to '''null '''or '''zero'''.

|So, type: '''int ''' ''' roll_no''' equal to '''50'''  next line '''String''' '''name''' equal to within double quotes '''Raju'''.

| | Now, '''save '''and '''run '''the file. Press '''Ctrl, S''' and '''Ctrl, F11'''.

|  We get the output as expected; '''The roll number is 50'''.  

|This is because we have explicitly initialized the variables  in the '''Student''' '''class'''.

|  We can see that here the '''fields '''have no '''modifier '''or ''' default modifier'''.

|  Recall '''modifiers''', we had discussed in '''Creating Classes.'''

|  We can see that, here, they are in the same '''default package'''.

| We will now change the '''modifier''' to '''private'''.

|  So, before the '''field''' declarations, type: '''private'''. So, type: '''private''' space '''int roll_no=50;'''.

|  Next line, '''private''' space '''String''' '''name = Raju;'''.

| Now '''save''' the file '''Student.java'''.

| 05:00

| We can see that we get errors in '''TestStudent.java'''.

| Hover the mouse over the error symbol.

| It says '''The field Student ''' dot '''roll number '''is not visible.

| And '''The field Student ''' dot '''name '''is not visible.

| This is because '''private fields''' can be accessed only within its own class.

| 05:52

| Now  '''Save''' the file and '''Run''' the program.

|  We see the output on the console. '''The Roll no is 50''' '''The name is Raju'''.

|  '''Instance fields''' are called so because their values are unique to each '''instance''' of a class.

|  Let us go back to the '''TestStudent class'''.

| Here, we will create one more object of the '''Student class'''.

| So, type: next line, '''Student''' space '''stud2''' equal to '''new''' space '''Student''' opening and closing brackets semicolon.

|  We will now initialize both the objects in the '''TestStudent class'''.

|  So, next line, type: '''stud1''' dot select '''roll_no'''  press ''' Enter''' equal to '''20 ''' semicolon.  

|  Next line, type: '''stud1''' dot select  '''name''' press '''Enter''' equal to within double quotes '''Ramu ''' semicolon press '''Enter'''.

|  Thus we have initialized the '''fields''' for the first object.

|  Now, we will initialize the '''fields''' for the second object.

|  So, type: '''stud2''' dot select '''roll_no''' equal to '''30 '''semicolon.

| Next line, '''stud2''' dot select '''name''' equal to within double quotes''' Shyamu ''' semicolon''' press''' Enter'''.

| 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.  

| '''System''' dot '''out''' dot '''println''' within brackets and double quotes '''The name is''', plus '''stud2 ''' dot select '''name''' and semicolon.

|  Now, '''save''' and''' run '''the file. Press ''' Ctrl, s''' and '''Ctrl, F11'''.  

| We get the output as follows.  '''The roll_no is 20''', '''The name is Ramu''' '''The roll_no is 30''', '''The name is shyamu'''.

|  Here, both '''stud1''' and '''stud2''' are referring to two different '''objects'''.

|  We can see that here.The first object has the values '''20''' and '''Ramu'''.

|  The second object has the values '''30 '''and '''Shyamu'''.

|  We will now print the values  of the third '''object'''.

| So, type: '''System''' dot '''out''' dot '''println''' within brackets and double quotes '''The  roll_no is''' plus '''stud3 ''' dot select '''roll_no''' semicolon.

|next line, type: '''System''' dot '''out''' dot '''println''' within brackets and double quotes '''The  name is''' plus '''stud3 ''' dot''' name''' semicolon.

 

|  This is because we had explicitly initialized the fields of the '''Student class''' to''' 50''' and ''' Raju'''.

|  Now, try de-initializing the '''field'''s 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 '''TestEmployee''' '''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.

| Use '''45''' and '''Sandeep''' as values for second object.

|12:31

|Display the 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 [http://spoken-tutorial.org/What_is_a_Spoken_Tutorial].  

 

|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

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| 12:52

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| 13:01

| Spoken Tutorial Project is a part of the Talk to a Teacher project.

| It is supported by the National Mission on Education through ICT, MHRD, Government of India.

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| 13:19

| Thus we have come to the end of this tutorial.

| This is Arya Ratish from IIT Bombay, signing off. Thanks for joining.