Example of abstract class in java

abstract class Person
{
    String name;
    int age;
    Person(String name,int age)
    {
        this.name=name;
        this.age=age;
    }
    void showbasicDetails()
    {
        System.out.println("Name :" + name);
        System.out.println("Age :"+ age);
    }
    abstract void showDetails();
}
class Employee extends Person
{
    String empid;
    int salary;
    Employee(String name,int age, String empid, int salary)
    {
        super(name,age);
        this.empid=empid;
        this.salary=salary;
    }
    void showDetails()
    {
        System.out.println("Empid : " + empid);
        System.out.println("Salary : "+ salary );
    }
}
class Student extends Person
{
    int regd_no;
    char grade;
    Student(String name,int age, int regd_no,char grade)
    {
        super(name,age);
        this.regd_no=regd_no;
        this.grade=grade;
    }
    void showDetails()
    {
        System.out.println("Student regd no : "+ regd_no);
        System.out.println("Student grade :" + grade);
    }
}
class PersonDemo
{
    public static void main(String[] args)
    {
        Person p1=new Employee("Dreek",20,"E 209", 1000000);
        p1.showbasicDetails();
        p1.showDetails();
        Person p2=new Student("Bikash",19,48, 'A');
        p2.showbasicDetails();
        p2.showDetails();       
    }
}