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Welcome to the Spoken Tutorial on parameterized constructor in java.

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In this tutorial we will learn:

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* About a parameterized constructor.

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* And to create a parameterized constructor.

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Here we are using:

 Ubuntu version 11.10 OS

 Java Development kit  1.6

 And  Eclipse 3.7.0

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To follow this tutorial, you must know

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how to create a default constructor in java using eclipse.

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If not, for relevant tutorials, please visit our website which is as shown.
http://www.spoken-tutorial.org

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What is a parameterized constructor?

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A constructor that has parameters is called a parameterized constructor.

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It can have one or more than one parameters.

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Let us now create a parameterized constructor.

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So in the eclipse, I have   Student.java file.

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We created this file in the previous tutorial.

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Now, inside the constructor we will give the variables their default value.

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So roll_number is equal to zero instead of ten.

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And name is equal to null instead of Raman.

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Then type System dot out dot println "I am a  default constructor".

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So, we have created a constructor with no parameters.

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In java, such constructor is also called a default constructor.

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Now we will create another constructor.

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So, type: Student parentheses.

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Inside parenthesis int the_roll_number comma String the_name.

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So, what we have done is declared a constructor with parameters.

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The name of the constructor is  Student that is the class name.

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Inside the parentheses, we have given two parameters to the constructor.

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We can give any number of parameters to the constructor.

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Now, inside curly brackets type:

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System dot out dot println "I am a parameterized constructor".

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Then, roll_number is equal to the_roll_number.

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And name is equal to the_name.

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So, we have created a   constructor with parameters.

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Now let's call this  constructor.

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So, in the main method type: student stu2 equal to new student within parentheses 11 comma in double quotes Raju.

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Let's call the studentDetail  method.

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So, type: stu2.studentDetail.

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Save and Run the program.

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We see the output on the console.

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The default constructor is called first.

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It initializes the variables to their default values.

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Then the parameterized constructor is called.

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It initializes the variables to the values that are passed as the arguments.

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That is 11 and Raju.

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Let us see how the parameterized constructor works.

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When we call the parameterized constructor, we pass two values  to it.

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These are called arguments.

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The value 11 is copied to the parameter the_roll_number.

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And  the  value Raju is copied  to the parameter the_name.

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Then the value of the_roll_number is assigned to roll_number.

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And the value of the_name is assigned to name.

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Hence,  in the  output  we see 11  and  Raju.

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Let us see the common errors when we call a parameterized constructor.

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Suppose, we pass a single argument to the constructor.

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So remove Raju.

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We get an error. It states that “The constructor Student with parameter (int) is undefined.”

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So, the number of arguments must match the number of parameters.

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Here we can retype Raju and resolve the error.

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Alternatively, what we can  do is define another constructor with a single parameter.

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Let us  do that.

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So, Student within parentheses int r_ number.

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Inside curly brackets, type:   System dot out dot println

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"I am a constructor with a single parameter".

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Then roll_number is equal to r_ number.

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Save the file.

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We see that the error is resolved  when we define the constructor.

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Let's  Run the program.

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On the console we see that the roll number is assigned the value 11.

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While name is null since the constructor takes only one argument.

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Let us now call back our constructor with two parameters.

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So, type Student stu3 is equal to new Student.

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11 comma Raju.

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Then Stu3 dot studentDetail.

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Suppose here we pass 11 as String, so add double quotes.

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We get an error.

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It states that “The constructor Student String comma String is undefined.”

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So even the data type of the argument must match with that of the parameter.

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So now remove the quotes and Save the file.

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Now we do not see an error.

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So  Run the program.

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In the output we see three constructors.

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The first one is the default constructor.

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The second one is the Constructor with one parameter.

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And this third one is the Constructor with two parameters.

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This is how we create parameterized constructor in java.

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Why constructor?

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The variables in a class must be initialized each time an instance is created.

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It can be tedious to initialize all the variables.

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So, java allows objects to initialize themselves when they are created.

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This is performed through the use of a constructor.

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So in this tutorial, we have learnt:

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* To create parameterized constructor.

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* Functionality of parameterized constructor.

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* And the advantage of using constructor.

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For self assessment, create a class Employee.

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Create constructors with different number of parameters.

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watch the video available at [1].

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[2].

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This brings us to the end of the tutorial.

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Thanks for joining.

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This is Prathamesh Salunke, signing off.
Jai Hind.