Abstract class Program which covers many concerpts

 klct class Student 

{

     int id;

    String name;

    int marks;

    Student()

    {

        id = 10;

        string name = "yourname";

        marks = 85;

    }

    Student(int i, String n, int m)

    {

        id = i;

        name = n;

        marks = m;

    }

    Student(Student s)

    {

        id = s.id;

        name = s.name;

        marks = s.marks;

    }

    abstract void displayName();

    void displayInfo() 

    {

        System.out.println("Student id: " + id);

        System.out.println("Student name: " + name);

        System.out.println("Student marks: " + marks);

    }

}

class Student1 extends Student

 {

    void displayName()

    {

        System.out.println("Student1 name: " + name);

    }

 }

class Student2 extends Student

 {

    void displayName() 

    {

        System.out.println("Student2 name: " + name);

    }

 }

class Student3 extends Student

 {

   

    String gender;

    Student3()

    {

        super();

    }

    Student3(int i, String n, int m, String g)

    {

        super(i, n, m);

        gender = g;

    }

    Student3(Student3 s) 

    {

        super(s);

        gender = s.gender;

    }

    void displayName()

    {

        System.out.println("Student1 name: " + name);

    }

   

}

public class StudentDemo

{

    public static void main(String[] args)

    {

        Student3 g = new Student3(1, "your name", 88, "f");

        Student A;

        A = g;

        A.displayInfo();

        Student1 obj1 = new Student1();

        Student2 obj2 = new Student2();

        Student3 ob1 = new Student3();

        Student3 ob2 = new Student3(1,"name",92,"f");

        Student3 ob3 = new Student3(ob1);

    

        //System.out.println("info="+ob1.gender);

    

        System.out.println("gender="+ob2.gender);

        //System.out.println("info="+ob3.gender);

          Student ref;

        ref = obj1;

        ref.displayName();

        ref.displayInfo();

        ref = obj2;

        ref.displayName();

        ref.displayInfo();

    }

}