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

|  Welcome to the Spoken Tutorial on '''using this keyword''' in '''java'''.

|  In this tutorial we will learn

|About use of '''this''' keyword

|  To use '''this''' keyword with '''fields'''

| To use '''this '''keyword for chaining of '''constructors'''.

 

 

 

|  Here we are using

 

 

|  To follow this tutorial you must know

|  how to create a '''  constructor''' in '''java''' using '''eclipse'''.

 

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

|Now  we will see the use of this '''key word'''

| Within a '''constructor''', '''this''' is a reference to the current '''object'''.

 

|  We can refer any member of the current '''object''' within a''' constructor''' using '''this'''.

|Now we will see the use of '''this''' keyword with '''fields'''.  

| '''this '''keyword helps us to avoid name conflicts.

 

|  We can see such an example here.

 

|  For that let us open '''Eclipse'''.

 

|  Open the '''Student class''' we had created in the earlier tutorial.

 

|  Comment the '''default constructor ''' comment the '''constructor''' with 1 parameter.

 

|  Also comment the code for creating the first two '''objects'''.

 

|  Now, notice the '''parameterized constructor.'''

 

|  '''the_roll_number''' and '''the_name '''are the  arguments passed to the constructor.

 

|  '''roll_number''' and '''name '''are the instance variables.

 

|  Now, let me change the arguments to '''roll_number''' and '''name''' itself.

 

|  So inside the '''constructor''' we have:

|  '''roll_number '''equal to''' roll_number''' and '''name '''equal to''' name.'''

 

|Now  '''Save '''and '''run '''the file.So press'''Ctrl ,S'''and '''Ctrl, F11'''

|  We get the  output as follows:

 

|   I am a Parameterized Constructor

''' 0

null'''

| Now come back to the  code.

| We  see 2 warnings in the code.

|  Hover  your mouse over the warning symbol.

|We can see  '''The assignment to the variable roll_number has no effect.'''

 

| And '''The assignment to the variable name has no effect.'''

 

|  This is because in the '''constructor roll_number and name''' are '''local variables'''.

 

|  '''Local variables''' are '''variables''' that are accessible within the '''method''' or '''block'''.

 

 

|  Here, '''roll_number''' and '''name''' will be initialized to '''11''' and '''Raju'''.

 

| Because we have passed the values '''11''' and '''Raju'''the constructor.

| But  once they come out of the '''constructor''', it is not accessible.

 

 

|  Then the only '''roll_number''' and '''name''' we know are the '''instance variables'''.

 

 

|  They have been initialized to '''0 '''and '''null '''already once the '''object''' is created.

 

 

|  So we got the output as '''0 '''and '''null'''.

 

|  Now, let us make a small change inside the constructor.

 

 

| So type '''this '''''dot '''''roll_number equal to roll_number'''.

 

 

|  And''' this '''''dot '''''name equal to name'''.

 

 

|  Now '''save '''and '''run''' the file. So press '''ctrl, S''' And '''Ctrl, F11''' keys

| We get the output as

 

 

|  I am Parameterized Constructor

Raju'''

|  This is because '''this '''''dot '''''roll_number '''and '''this '''''dot '''''name''' refers to the '''instance variables''' '''roll_number''' and '''name.'''

 

 

|And here  '''roll_number '''and '''name '''are the arguments passed in the method.

 

 

|  To avoid confliction between '''local''' and '''instance''' variables we use '''this '''keyword.

|  Now we will see the use of '''this keywords''' for chaining of constructor.

|  We can use '''this '''keyword inside a '''constructor''' to call another one.

 

 

|  The '''constructors''' must be in the same '''class.'''

 

 

|  This is called '''explicit constructor invocation'''.

| So let us come back to the''' Student '''class which we created.

|Now  Remove the comments.

| Now  comment the part to assign the '''instance variables to their values in the first two constructors.'''

 

 

|Then  Comment the part which creates the''' '''second and third '''objects.'''

| Now  let us first come to the  constructor with no parameters.

 

 

|  After  curly brackets type '''this''' within brackets '''11''' and  ''semicolon''.

| Inside the second '''constructor''' type '''this''' within brackets '''11''' ''comma'' within double quotes '''Raju''' ''semicolon''.

| Now '''Save''' and '''Run''' the file. So press '''Ctrl,S''' and '''Ctrl , F11'''.

|  We get the output as

 

 

'''11''' and

 

| Now, I will explain the output.

 

 

|  When the object is created, the respective constructor gets called.

 

 

|  The '''constructor''' here is the '''no argument constructor'''.

 

 

|  The control comes to the first line in the '''constructor'''.

 

 

| It encounters the '''this '''''within brackets '''''11''' statement.

 

 

|  Hence it calls the constructor that accepts single integer argument.

 

 

|  Then the control comes to '''this '''''within brackets''''' 11 '''''comma '''''Raju.'''

 

 

|  Hence it calls the constructor that accepts 1 '''integer''' and 1 '''String''' argument.

 

 

|  So this '''constructor''' is executed and we get the output as '''I am Parameterized Constructor'''.

 

 

|Now  the instance variables will be initialized to  '''11''' and '''Raju.'''As we have passed.

 

 

|  Now, the control goes back to the calling '''constructor'''.

 

 

|  So the second''' constructor ''' gets executed.

 

 

|  We get the output as''' I am constructor with a single parameter.'''

 

 

|  Then, the control goes to the first constructor and executes it.

 

 

|  So we get output as''' I am a default constructor.'''

 

 

|  Then '''studentDetail method''' is executed.

 

 

|  So, we get '''11 '''and '''Raju'''.

|  Now, let us make a small change.

 

 

| Make the '''this''' statement the last one in the constructor.

 

 

|  We get  a compiler error.

 

 

|  Hover the mouse over the error symbol.

 

 

|  We get the error as:

 

 

|  So we must make it the first line of the '''constructor.'''

| So make it the first line of the '''constructor.'''

 

 

|  Now we can see that the error has gone.

|  So in this tutorial, we  learnt

 

|  To use''' this''' keyword with''' fields.'''

 

| To use''' this''' keyword for chaining '''constructors'''

 

|  How '''this '''keyword should be used within a''' constructor.'''

 

 

 

|  For self assessment, in the '''Employee class''' created earlier:

 

|  Create a '''constructor''' with two parameters

|  Use''' this '''keyword to initialize the''' instance variables .'''

|  Also create a '''constructor''' with 1 and no parameters.

|  Try chaining the '''constructors '''using '''this''' as explained in the tutorial.

 

 

|  To know more about the Spoken Tutorial Project

|   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]  

|   It summarizes the Spoken Tutorial project

 

|  If you do not have good bandwidth, you can download and watch it

 

 

|  The Spoken Tutorial Project Team

 

|  Conducts workshops using spoken tutorials

 

| Gives certificates for those who pass an online test

 

|  For more details, please write to contact@spoken-tutorial.org  

 

 

|  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

 

|  More information on this Mission is available at

 

* [http://spoken-tutorial.org/NMEICT-Intro http://spoken-tutorial.org/NMEICT-Intro]

 

 

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

 

 

 

|  This is Arya Ratish signing off. Thanks for joining.