Difference between revisions of "Java/C2/Parameterized-constructors/English-timed"

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Revision as of 22:11, 31 March 2015

Time Narration
00:02 Welcome to the Spoken Tutorial on parametrized constructor in java.
00:08 In this tutorial we will learn:
00:10 * About a parametrized constructor.
00:13 * And to create a parametrized constructor.
00:17 Here we are using:
  • Ubuntu version 11.10 OS
  • Java Development kit 1.6
  • And Eclipse 3.7.0
00:29 To follow this tutorial, you must know
00:32 how to create a default constructor in java using eclipse.
00:37 If not, for relevant tutorials, please visit our website which is as shown.

http://www.spoken-tutorial.org

00:44 What is a parametrized constructor?
00:48 A constructor that has parameter is called a parametrized constructor.
00:55 It can have one or more than one parameters.
00:59 Let us now create a parametrized constructor.
01:03 So in the eclipse, I have Student.java file.
01:09 We created this file in the previous tutorial.
01:15 Now, inside the constructor we will give the variables their default value.
01:21 So roll_number is equal to zero instead of ten.
01:27 And name is equal to null instead of Raman.
01:33 Then type System dot out dot println I am a default constructor.
01:55 So, we have created a constructor with no parameters.
02:00 In java, such constructor is also called a default constructor.
02:07 Now we will create another constructor.
02:11 So, type: Student parentheses.
02:17 Inside parenthesis int the_roll_number comma String the_name.
02:36 So, what we have done is declared a constructor with parameters.
02:43 The name of the constructor Student that is the class name.
02:49 Inside the parentheses, we have given two parameters to the constructor.
02:57 We can give any number of parameters to the constructor.
03:02 Now, inside curly brackets type:
03:05 System dot out dot println I am a parametrized constructor.
03:29 Then, roll_number is equal to the_roll_number.
03:43 And name is equal to the_name.
03:53 So, we have created a constructor with parameters.
03:58 Now let's call this constructor.
04:02 So, in the main method type: student stu2 equal to new student within parentheses 11 comma in double quotes Raju.
04:28 Let's call the studentDetail method.
04:31 So, type: stu2.studentDetail.
04:38 Save and Run the program.
04:44 We see the output on the console.
04:48 The default constructor is called first.
04:52 It initializes the variables to their default value.
04:56 Then the parametrized constructor is called.
05:00 It initializes the variables to the values that are passed as the arguments.
05:05 That is 11 and Raju.
05:08 Let us see how the parametrized constructor works.
05:12 When we call the parametrized constructor, we pass two values to it.
05:18 These are called arguments.
05:22 The value 11 is copied to the parameter the_roll_number.
05:31 And the value Raju is copied to the parameter the_name.
05:41 Then the value of the_roll_number is assigned to roll_number.
05:50 And the value of the_name is assigned to name.
05:55 Hence in the output we see 11 and Raju.
06:00 Let us see the common errors when we call a parametrized constructor.
06:07 Suppose we pass a single argument to the constructor.
06:11 So remove Raju.
06:15 We get an error. It states that “The constructor Student with parameter (int) is undefined.”
06:24 So, the number of arguments must match the number of parameters.
06:30 Here we can retype Raju and resolve the error.
06:36 Alternatively, what we can do is define another constructor with a single parameter.
06:42 Let us do that.
06:45 So, Student within parentheses int r_ number.
07:01 Inside curly brackets, type: System dot out dot println
07:13 I am a constructor with a single parameter.
07:29 Then roll_number is equal to r_ number.
07:48 Save the file.
07:51 We see that the error is resolved when we define the constructor.
07:58 Let's Run the program.
08:02 On the console we see that the roll number is assigned the value 11.
08:08 While name is null since the constructor takes only one argument.
08:18 Let us now call back our constructor with two parameters.
08:23 So, type Student stu3 is equal to new Student.
08:40 11 comma Raju.
08:46 Then Stu3 dot studentDetail.
08:58 Suppose here we pass 11 as String, so add double quotes.
09:08 We get an error.
09:10 It states that “The constructor Student String comma String is undefined.”
09:17 So even the data type of the argument must match with that of the parameter.
09:25 So now remove the quotes and Save the file.
09:32 Now we do not see an error.
09:35 So Run the program.
09:38 In the output we see three constructors.
09:42 The first one is the default constructor.
09:45 The second one is the Constructor with one parameter.
09:50 And this third one is the Constructor with two parameters.
09:56 This is how we create Parametrized constructor in java.
10:05 Why constructor?
10:07 The variables in a class must be initialized each time an instance is created.
10:13 It can be tedious to initialize all the variables.
10:18 So, java allows objects to initialize themselves when they are created.
10:25 This is performed through the use of a constructor.
10:30 So in this tutorial, we have learnt:
10:33 * To create parametrized constructor.
10:36 * Functionality of parametrized constructor.
10:39 And the advantage of using constructor.
10:44 For self assessment, create a class Employee.
10:48 Create constructors with different number of parameters.
10:53 To know more about the Spoken Tutorial project,
10:56 watch the video available at [1]
11:02 It summarizes the Spoken Tutorial project.
11:06 If you do not have good bandwidth, you can download and watch it.
11:10 The Spoken Tutorial project team:
11:12 Conducts workshops using spoken tutorials.
11:14 Gives certificates for those who pass an online test.
11:18 For more details, please write to contact@spoken-tutorial.org
11:24 Spoken Tutorial Project is a part of the Talk to a Teacher project.
11:28 It is supported by the National mission on Education through ICT, MHRD, Government of India.
11:34 More information on this Mission is available at:

[2]

11:43 This brings us to the end of the tutorial.
11:46 Thanks for joining.
11:47 This is Prathamesh Salunke, signing off.

Jai Hind.

Contributors and Content Editors

Gaurav, PoojaMoolya, Ranjana, Sandhya.np14, Sneha

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