Java/C2/Constructor-overloading/English

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Title of script: Constructor overloading

Author: Prathamesh Salunke

Keywords: video tutorial, constructor, overloading


Visual Cue
Narration
Slide 1

Opening slide

Welcome to the Spoken Tutorial on constructor overloading in java.
Slide 2

Learning Objectives

In this tutorial we will learn

- what is constructor overloading

- To overload constructor



Slide 3

System Requirements

Here we are using
  • Ubuntu version 11.10
  • Java Development Environment jdk 1.6
  • Eclipse 3.7


Slide 4

Prerequisites

To follow this tutorial you must know

how to create constructors in java using eclipse.


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

(http://www.spoken-tutorial.org)

Slide 5

Constructor Overloading

Define multiple constructors which differ in number or types of parameters.
Switch to Eclipse Let us now see how to overload constructor.

In eclipse, I have a class Student with two variables and a method.

Type:

Student(int number, String the_name)

{

roll_number=number;

name=the_name;

}

Let us first create a parameterized constructor.

So type, Student within parentheses int number comma String the_name.

Within curly brackets, roll_number is equal to number.

And name is equalto the_name


So we have a constructor with two parameters.

Type:

new Student();

Now let us call the constructor.

So type new Student parentheses semi colon

Point to the Error. We see an error that the constructor Student is not defined.

This is simply because we have defined a constructor with parameters.

And we are calling a constructor without parameters.

Type:

Student(22,”Ram”);

So let us pass arguments.

Type 22 comma in double quotes Ram.

We see that the error is resolved.

Type:

Student s = new Student(22,”Ram”);

s.studentDetail();

Let us call the method.

So before new type Student s is equal to.

Then s dot studentDetail();

Save and Run Save and Run the program.
Point to the Output We see the output 22 and Ram.
Type:

Student()

{

roll_number=0;

name=”-”;

}

Now let us define a default constructor.

So type, Student parentheses.

Within curly brackets roll_number is equal to 0.

And name is equal to in double quotes hypen.

Type:

Student s2 = new Student();


So now we can call the constructor with no parameters.

So type Student s1 is equal to new Student parentheses.

Type:

s2.studentDetail();

Then s1 dot studentDetail.
Save and Run Save and Run the program.
Point to the Output We see the output zero and dash when default constructor is called.

This is constructor overloading.

We have two constructor with difference in parameter.

Both the constructor obviously have same name.

So depending on the type and number of parameter, the constructor is called.

Type:

Student s3=new Student(“Raju”,45);

Let us see the advantage of constructor overloading.

Suppose when we call a constructor with two parameters.

So type Student s3= new Student();

And suppose if we pass the name argument first and then the roll number.

That is in double quotes Raju comma 45

Point to the Error We see an error that constructor String comma int is not defined.
Type:

Student(String the_name, int r_no)

{

roll_number=r_no;

name=the_name;

}

So let us define the constructor.

So type Student within parentheses String the_name comma int r_no

Within curly bracket, roll_number is equal to r_no.

And name is equal to the_name.

Save the file Save the file.

We see that the error is resolved.

Type:

s3.studentDetail();

Now call the method.

So type, s3 dot studentDetail.

Save and Run Save and Run the file.
Point to the Output We see 45 and Raju on the console.

So here we see that when we call the constructor.

We do not have to worry about the parameters we are passing.

This is because we have define multiple constructor with different parameters.

So the proper constructor is overloaded.

Type:

Student(int num)

{

roll_number=num;

}

We can therefore define constructor which takes only one parameter.

That is roll number.

So type Student within parentheses int num.

Then within curly brackets roll_number is equalto num.

And name is equal to in double quotes no name.

Student s4 = new Student(61);

s4.studentDetail();

So now when we call the constructor and give one integer argument.

So type Student s4 is equalto new Student within parentheses 61

Then s4 dot studentDetail

Save and Run the program Save and Run the program
Point to the Output So in the output we see roll number as 61 and name as no name.

As we can see, the proper overloaded constructor is called when new is executed.

Based upon the parameters specified the proper constructor is overloaded.

This is how constructor overloading is done.

Slide 6

Summary

So in this tutorial, we have learnt

What is constructor overloading.

How to overload constructor.



Slide 7

Assignment

For self assessment, create multiple constructors for class Employee.

Overload the constructor.



Slide 8

About Slide

To know more about the Spoken Tutorial Project
  • If you do not have good bandwidth, you can download and watch it


Slide 9

About Slide


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Slide 10

Acknowledgment

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


We have come to the end of this tutorial.

Thanks for joining.

This is Prathamesh Salunke signing off.

Jai Hind.

Contributors and Content Editors

Chandrika

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