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

|| ''Time'''

|  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

 

*Ubuntu version 11.10

*jdk 1.6

*Eclipse 3.7.0  

| 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'''.  

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

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

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

|Now Save and run the file.So pressCtrl ,Sand Ctrl, F11

| ''' I am a Parameterized Constructor

 

|  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.  

| 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.  

|  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'''

|  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'''.  

|   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   

|   '''I am a Parameterized Constructor'''

|   '''I am a constructor with a single parameter'''

|   '''I am Default Constructor'''

| Now, I will explain the output.  

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

| It encounters the this within brackets 11 statement.  

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

|  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.  

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

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

|  '''Constructor''' call must be the first statement in the '''constructor'''.

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

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

|  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

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| 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  

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