Java Encapsulation: Implementing a Student Class with Grade Validation

Java Encapsulatiion: Exercise-7 with Solution

Write a Java program to create a class called Student with private instance variables student_id, student_name, and grades. Provide public getter and setter methods to access and modify the student_id and student_name variables. However, provide a method called addGrade() that allows adding a grade to the grades variable while performing additional validation.

Sample Solution:

Java Code:

// Student.java
// Student Class

import java.util.ArrayList;
import java.util.List;

class Student {
  private int student_id;
  private String student_name;
  private List < Double > grades;

  public int getStudent_id() {
    return student_id;
  }

  public void setStudent_id(int student_id) {
    this.student_id = student_id;
  }

  public String getStudent_name() {
    return student_name;
  }

  public void setStudent_name(String student_name) {
    this.student_name = student_name;
  }

  public List < Double > getGrades() {
    return grades;
  }

  public void addGrade(double grade) {
    if (grades == null) {
      grades = new ArrayList < > ();
    }
    grades.add(grade);
  }
}

// Main.java
// Main Class
import java.util.ArrayList;
import java.util.List;
public class Main {
  public static void main(String[] args) {
    // Create an instance of Student
    Student student = new Student();

    // Set the values using the setter methods
    student.setStudent_id(1);
    student.setStudent_name("Nadia Hyakinthos");

    // Add grades using the addGrade() method
    student.addGrade(92.5);
    student.addGrade(89.0);
    student.addGrade(90.3);

    // Get the values using the getter methods
    int student_id = student.getStudent_id();
    String student_name = student.getStudent_name();
    List < Double > grades = student.getGrades();

    // Print the values
    System.out.println("Student ID: " + student_id);
    System.out.println("Student Name: " + student_name);
    System.out.println("Grades: " + grades);
  }
}

Sample Output:

Student ID: 1
Student Name: Nadia Hyakinthos
Grades: [92.5, 89.0, 90.3]

Explanation:

In the above exercise,

The Student class:

• It defines a class called Student with private instance variables student_id, student_name, and grades.
• The variables are marked as private, which means they can only be accessed within the Student class.
• Public getter and setter methods are provided for student_id and student_name to access and modify these variables.
• Additionally, a getter method is provided for the grades variable, which returns a list of double values.
• There is also a method called addGrade() that allows adding grades to the grades list. It performs additional validation by checking if the grades list is null and initializing it if necessary.

The Main class:

• It contains the main method, which serves as the entry point for the program.
• An instance of the Student class is created using the new keyword.
• The values of student_id and student_name are set using the setter methods.
• Grades are added to the grades list using the addGrade() method.
• The values of student_id, student_name, and grades are retrieved using the respective getter methods.

Flowchart:

Java Code Editor:

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