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Test Student Marks Using Private Keyword - Java Example Program


Test Student Marks Using Private Keyword
class TestStudentMarksImproved
{
    public static void main(String arg[])
    {
        Student madhavan = new Student("Madhavan");
        
        madhavan.setMarks(87, 65, 93);
        
        System.out.println("Subject 1 = " + madhavan.getSubject1Marks());
        System.out.println("Subject 2 = " + madhavan.getSubject2Marks());
        System.out.println("Subject 3 = " + madhavan.getSubject3Marks());
        System.out.println("Total = " + madhavan.getTotalMarks());
        
        
        // LINE X - THROWS COMPILATION ERROR
        // madhavan.subject1 = 87;
        // LINE Y - THROWS COMPILATION ERROR
        // System.out.println("Subject 1 = " + madhavan.subject1);
        
    
    }
}

class Student
{
    private String name;
    private int subject1;
    private int subject2;
    private int subject3;
    private int total_marks;

    Student(String name)
    {
        this.name = name;
    }

    void setMarks(int subject1, int subject2, int subject3)
    {
        this.subject1 = subject1;
        this.subject2 = subject2;
        this.subject3 = subject3;

        this.total_marks = subject1 + subject2 + subject3; // LINE A
    }

    int getSubject1Marks()
    {
        return subject1; // LINE B
    }

    int getSubject2Marks()
    {
        return subject2;
    }

    int getSubject3Marks()
    {
        return subject3;
    }

    int getTotalMarks()
    {
        return total_marks;
    }
}
OUTPUT

Subject 1 = 87
Subject 2 = 65
Subject 3 = 93
Total = 245

DESCRIPTION

In this program we have used the private keyword. private is an access specifier which prevents a member variable to be accessed from outside the class. e.g., The member variable subject1 is only accessible inside the class Student. If we try to access it from main method in the class TestStudentMarksImproved, it will throw a compilation error.

THINGS TO TRY
  • Uncomment the LINE X and LINE Y and observe the compilation error you get.
  • After uncommenting the LINE X and LINE Y and also remove the private access specifier for subject1 and see that the program compiles with out any error.

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