What is the use of parametrized constructor in Java?

A constructor is similar to method and it is invoked at the time creating an object of the class, it is generally used to initialize the instance variables of a class. The constructors have same name as their class and, have no return type.

There are two types of constructors parameterized constructors and no-arg constructors a parameterized constructor accepts parameters.

The main purpose of a constructor is to initialize the instance variables of a class. Using a parameterized constructor, you can initialize the instance variables dynamically with the values specified at the time of instantiation.

public class Sample{
   Int i;
   public sample(int i){
      this.i = i;
   }
}

Example

In the following example the Student class has two private variables age and, name. From main method we are instantiating the class variables using parameterized constructors −

Live Demo

import java.util.Scanner;
public class StudentData {
   private String name;
   private int age;
   //parameterized constructor
   public StudentData(String name, int age){
      this.name =name;
      this.age = age;
   }  
   public void display(){
      System.out.println("Name of the Student: "+this.name );
      System.out.println("Age of the Student: "+this.age );
   }
   public static void main(String args[]) {
      //Reading values from user
      Scanner sc = new Scanner(System.in);      
      System.out.println("Enter the name of the student: ");
      String name = sc.nextLine();
     
      System.out.println("Enter the age of the student: ");
      int age = sc.nextInt();      
      System.out.println(" ");
     
      //Calling the parameterized constructor
      new StudentData(name, age).display();
   }
}

Output

Enter the name of the student:
Sundar
Enter the age of the student:
20

Name of the Student: Sundar
Age of the Student: 20