import java.util.*; /**  * This program demonstrates abstract classes.  * @version 1.01 2004-02-21  * @author Cay Horstmann  */ public class PersonTest {    public static void main(String[] args)    {       Person[] people = new Person[2];       // fill the people array with Student and Employee objects       people[0] = new Employee("Harry Hacker", 50000, 1989, 10, 1);       people[1] = new Student("Maria Morris", "computer science");       // print out names and descriptions of all Person objects       for (Person p : people)          System.out.println(p.getName() + ", " + p.getDescription());    } } abstract class Person {    public Person(String n)    {       name = n;    }    public abstract String getDescription();    public String getName()    {       return name;    }    private String name; } class Employee extends Person {    public Employee(String n, double s, int year, int month, int day)    {       super(n);       salary = s;       GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);       hireDay = calendar.getTime();    }    public double getSalary()    {       return salary;    }    public Date getHireDay()    {       return hireDay;    }    public String getDescription()    {       return String.format("an employee with a salary of $%.2f", salary);    }    public void raiseSalary(double byPercent)    {       double raise = salary * byPercent / 100;       salary += raise;    }    private double salary;    private Date hireDay; } class Student extends Person {    /**     * @param n the student's name     * @param m the student's major     */    public Student(String n, String m)    {       // pass n to superclass constructor       super(n);       major = m;    }    public String getDescription()    {       return "a student majoring in " + major;    }    private String major; }

 for (Person p : people)          System.out.println(p.getName() + ", " + p.getDescription());