Difference between revisions of "Java/C2/Constructor-overloading/English-timed"

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Revision as of 14:52, 8 April 2015


Time Narration
00:03 Welcome to the Spoken Tutorial on constructor overloading in java.
00:08 In this tutorial, we will learn
00:10 what is constructor overloading
00:13 and to overload constructor.
00:16 Here we are using:
  • Ubuntu version 11.10 OS
  • Java Development kit 1.6
  • Eclipse 3.7.0
00:27 To follow this tutorial, you must know
00:30 how to create constructors in java using eclipse.
00:34 If not, for relevant tutorials, please visit our website which is as shown.

http://www.spoken-tutorial.org

00:40 What is constructor overloading?
00:43 Define multiple constructors for a class.
00:46 They must differ in number or types of parameters.
00:50 Let us now see how to overload constructor.
00:54 In eclipse, I have a class Student with two variables and a method.
01:03 Let us first create a parameterized constructor.
01:07 So, type: Student within parentheses int number comma String the_name.
01:26 Within curly brackets, type: roll_number is equal to number.
01:38 And name is equal to the_name
01:46 So, we have a constructor with two parameters.
01:51 Let us call this constructor.
01:53 So, in main method type: new Student parentheses semicolon.
02:03 We see an error, it states that constructor Student is undefined.
02:10 This is simply because we have defined a constructor with two parameters.
02:16 And we are calling a constructor without parameters.
02:22 So, we need to pass arguments.
02:25 So, within parentheses type: 22 comma in double quotes Ram.
02:33 We see that the error is resolved.
02:36 Let us call the method.
02:38 So, before new , type: Student s is equal to new student.
02:45 Now, using the object s we will call the method studentDetail().
02:53 Save the program and Run.
02:58 We see the output: 22 and Ram.
03:03 Now let us define a constructor with no parameter.
03:07 So, type: Student parentheses.
03:12 Within curly brackets roll_number is equal to 0.
03:21 And name is equal to in double quotes hyphen that is no name.
03:30 So, now we can call the constructor with no parameters.
03:35 So, type: Student s1 is equal to new Student parentheses semicolon.
03:47 This time we see no error, since we have defined a constructor without parameter.
03:55 Then s1 dot studentDetail();.
04:01 Save and Run the program.
04:04 So, in the output we see zero and dash when the default constructor is called.
04:11 This is constructor overloading.
04:13 We have two constructors with different parameters.
04:17 Both the constructors obviously have same name.
04:20 So, depending on the type and number of parameters, the constructor is called.
04:26 Let us see the advantage of constructor overloading.
04:30 Suppose, now we call a constructor with two parameters.
04:35 So, type: Student s3= new Student();
04:51 Now within parentheses, suppose I gave the name argument first and then the roll_number.
04:58 Let's see what happens.
04:59 So, in double quotes Raju comma 45.
05:08 We see an error which states that "The constructor Student with the parameter String comma int is undefined."
05:18 So, let us first define the constructor.
05:22 So, type: Student within parentheses String the_name comma int r_no.
05:42 So, over here first parameter is string and the second parameter is int.
05:52 Then, within curly bracket, roll_number is equal to r_no;
06:05 and name is equal to the_name;
06:15 Save the program.
06:18 Now we see that the error is resolved.
06:22 Let us call the method.
06:24 So, s3 dot studentDetail();
06:29 Save the program and Run.
06:35 So, we see the output 45 and Raju.
06:40 So, here we see that when we call the constructor
06:43 we do not have to worry about the parameters that we are passing.
06:47 This is simply because we have defined multiple constructors with different parameters.
06:54 So, the proper constructor is overloaded.
06:57 We can therefore now define a constructor which takes only one parameter.
07:02 That is roll number.
07:05 So, type: Student within parentheses int num,
07:16 within curly brackets roll_number is equal to num.
07:25 And name is equal to "no name".
07:33 Now, let us call this constructor.
07:43 So, type: Student s4 is equal to new Student;. This time we will pass a single argument. So, let us pass 61.
08:04 Then s4 dot studentDetail();
08:10 Save and Run the program.
08:14 So, in the output we see the roll number as 61 and name as no name.
08:21 As we can see, the proper overloaded constructor is called when new is executed.
08:27 Based upon the parameters specified, the proper constructor is overloaded.
08:33 This is how constructor overloading is done.
08:40 So, in this tutorial, we have learnt:
08:42 * About the constructor overloading
08:45 * To overload constructor and the use of constructor overloading
08:50 For self assessment, create multiple constructors for class Employee and overload the constructor.
08:58 To know more about the Spoken Tutorial project,
09:00 watch the video available at [1].
09:06 It summarizes the Spoken Tutorial project.
09:09 If you do not have good bandwidth, you can download and watch it.
09:12 The Spoken Tutorial project team:
09:15 Conducts workshops using spoken tutorials.
09:17 Gives certificates to those who pass an online test.
09:20 For more details, please write to contact@spoken-tutorial.org
09:26 Spoken Tutorial Project is a part of the Talk to a Teacher project.
09:30 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
09:35 More information on this mission is available at

[2].

09:43 This brings us to the end of the tutorial.
09:46 Thanks for joining.
09:47 This is Prathamesh Salunke, signing off. Jai Hind.

Contributors and Content Editors

Devisenan, Gaurav, PoojaMoolya, Sandhya.np14, Sneha