Abstract Classes in java-CFANZ编程社区

Could you have omitted the abstract method altogether from the Person superclass, simply defining the getDescription methods in the Employee and Student subclasses?
If you want did that, then you wouldn’t have been able to invoke the getDescription method on the variable p.
The compiler ensures that you invoke only methods that are declared in the class.

package abstractClasses;

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());
    }
}

// Enables transform audio video link to to html5 embed audio video tags.
package abstractClasses;

public abstract class Person 
{
    public abstract String getDescription();

    private String name;

    public Person(String n) 
    {
        name = n;
    }

    public String getName() 
    {
        return name;
    }
}

// Enables transform audio video link to to html5 embed audio video tags.
package abstractClasses;

import java.util.Date;
import java.util.GregorianCalendar;

public class Employee extends Person{
    private double salary;
    private Date hireDay;

    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;
    }
}

package abstractClasses;

public class Student extends Person{
    private String major;

    /**
     * @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;
    }
}