Question

We encourage you to work in pairs for this challenge to create a Student class with constructors.

1. First, brainstorm in pairs to do the Object-Oriented Design for a Student class. What data should we store about Students? Come up with at least 4 different instance variables. What are the data types for the instance variables?

2. Write a Student class below that has your 4 instance variables and write at least 3 different constructors: one that has no parameters and initializes the instance variables to default values, one that has 4 parameters to set the instance variables, and one that has 1 parameter for the most important instance variable and uses defaults for the others.

3. Add a print() method that uses System.out.println to print out all the instance variables.

4. Add a main method that constructs at least 3 Student objects using the 3 different constructors and then calls their print() methods.

5. /** class Student
   * with 4 instance variables,
   * 3 constructors, a print method,
   * and a main method to test them.
   */
   public class Student
   {
   // Write 4 instance variables

   
   // Write 3 constructors to initialize the instance variables
   // 1. no parameters using default values
   // 2. 1 parameter and the rest default values
   // 3. 4 parameters

   
   // Write a print method that prints all the instance variables
   public void print()
   {

   
   }

   // main method
   public static void main(String[] args)
   {
   // Construct 3 Student objects using the 3 different constructors

   
   // call their print() methods

   }
   }
   

Answer 1

Basic details of a Student is Name, age, Rollno and branch. Consider the below example instance variables and their data types.

Name - It is a string value

Age - It is integer value

Roll-no - It is a string value

Branch - It is a String value

Constructor:

constructors are the methods used to initialise the instace variables/objects of a class. when an object is created for a class then automatically constructor is called.

Program:

public class Student
{
   String name;
   int age;
   String rollno;
   String branch;
  
   public Student() //Default Constructor
   {
       this.name="Hari";
       this.age=20;
       this.rollno="5R3";
       this.branch="IT";      
   }

   public Student(String name) //Parameterised constructor with 1 parameter
   {
       this.name=name;
       this.age=25;
       this.rollno="5R3";  
       this.branch="CSE";
      
   }

   public Student(String name,int age,String rollno,String branch) //Parameterised constructor with 4 parameters
   {
       this.name=name;
       this.age=age;
       this.rollno=rollno;
       this.branch=branch;
   }
// print method to display the instace variables
   public void print()
   {
       System.out.println("Student Details:");
       System.out.println("Name: "+this.name);
       System.out.println("Age: "+this.age);
       System.out.println("Roll-No: "+this.rollno);
       System.out.println("Branch: "+this.branch);
       System.out.println();
      
   }
   public static void main(String args[])
   {
       Student s1=new Student();
       Student s2=new Student("Sri");
       Student s3=new Student("Hareesh",20,"5d3","ECE");
       s1.print();
       s2.print();
       s3.print();
   }
  
}

Output:

E:\>javac Student.java

E:\>java Student
Student Details:
Name: Hari
Age: 20
Roll-No: 5R3
Branch: IT

Student Details:
Name: Sri
Age: 25
Roll-No: 5R3
Branch: CSE

Student Details:
Name: Hareesh
Age: 20
Roll-No: 5d3
Branch: ECE

Explanation:

In Object oriented programming, when an object is created for a class, complier searches for a constructor to execute, after that only it xecutes other methods. Here we created 3 different constuctors with 0 parameters, 1 parameter, 4 parameters respectively. If we do not pass arguments to the constructors, it take the default values.