public abstract class Employee {
   private String firstName;
   private String lastName;

   // constructor
   public Employee( String first, String last )
   {
      firstName = first;
      lastName = last;
   }
   
   // get first name
   public String getFirstName() 
   { 
      return firstName; 
   }

   // get last name
   public String getLastName()
   { 
      return lastName; 
   }

   public String toString()
   { 
      return firstName + ' ' + lastName; 
   }

   // Abstract method that must be implemented for each 
   // derived class of Employee from which objects 
   // are instantiated.
   public abstract double earnings(); 

}  // end class Employee

public final class Boss extends Employee {
   private double weeklySalary; 

   // constructor for class Boss
   public Boss( String first, String last, double salary )
   {
      super( first, last );  // call superclass constructor
      setWeeklySalary( salary );
   }
   
   // set Boss's salary
   public void setWeeklySalary( double salary )
   { 
      weeklySalary = ( salary > 0 ? salary : 0 ); 
   }
   
   // get Boss's pay
   public double earnings() 
   { 
      return weeklySalary; 
   }
   
   // get String representation of Boss's name
   public String toString() 
   {
      return "Boss: " + super.toString();
   }
}  // end class Boss

public final class CommissionWorker extends Employee {
   private double salary;      // base salary per week
   private double commission;  // amount per item sold
   private int quantity;       // total items sold for week

   // constructor for class CommissionWorker
   public CommissionWorker( String first, String last,
      double salary, double commission, int quantity )
   {
      super( first, last );  // call superclass constructor
      setSalary( salary );
      setCommission( commission );
      setQuantity( quantity );
   }
   
   // set CommissionWorker's weekly base salary
   public void setSalary( double weeklySalary )
   { 
      salary = ( weeklySalary > 0 ? weeklySalary : 0 ); 
   }
   
   // set CommissionWorker's commission
   public void setCommission( double itemCommission ) 
   { 
      commission = ( itemCommission > 0 ? itemCommission : 0 );
   }
   
   // set CommissionWorker's quantity sold
   public void setQuantity( int totalSold )
   { 
      quantity = ( totalSold > 0 ? totalSold : 0 ); 
   }
   
   // determine CommissionWorker's earnings
   public double earnings()
   {
      return salary + commission * quantity; 
   }
   
   // get String representation of CommissionWorker's name 
   public String toString() 
   {
      return "Commission worker: " + super.toString();
   }

}  // end class CommissionWorker

public final class PieceWorker extends Employee {
   private double wagePerPiece; // wage per piece output
   private int quantity;        // output for week

   // constructor for class PieceWorker
   public PieceWorker( String first, String last,
      double wage, int numberOfItems )
   {
      super( first, last );  // call superclass constructor
      setWage( wage );
      setQuantity( numberOfItems );
   }
   
   // set PieceWorker's wage
   public void setWage( double wage ) 
   { 
      wagePerPiece = ( wage > 0 ? wage : 0 ); 
   }
   
   // set number of items output
   public void setQuantity( int numberOfItems ) 
   { 
      quantity = ( numberOfItems > 0 ? numberOfItems : 0 ); 
   }
   
   // determine PieceWorker's earnings
   public double earnings()
   { 
      return quantity * wagePerPiece; 
   }
   
   public String toString()
   {
      return "Piece worker: " + super.toString();
   }  

}  // end class PieceWorker

public final class HourlyWorker extends Employee {
   private double wage;   // wage per hour
   private double hours;  // hours worked for week

   // constructor for class HourlyWorker
   public HourlyWorker( String first, String last, 
      double wagePerHour, double hoursWorked )
   {
      super( first, last );   // call superclass constructor
      setWage( wagePerHour );
      setHours( hoursWorked );
   }
   
   // Set the wage
   public void setWage( double wagePerHour )
   { 
      wage = ( wagePerHour > 0 ? wagePerHour : 0 ); 
   }
   
   // Set the hours worked
   public void setHours( double hoursWorked )
   { 
      hours = ( hoursWorked >= 0 && hoursWorked < 168 ?
         hoursWorked : 0 ); 
   }
   
   // Get the HourlyWorker's pay
   public double earnings() { return wage * hours; }
   
   public String toString() 
   {
      return "Hourly worker: " + super.toString();
   }
}  // end class HourlyWorker

import java.text.DecimalFormat;
import java.awt.*;
import java.applet.*;

public class PayrollApplet extends Applet {

   // test Employee hierarchy
   public void init() {
   
      TextArea ta;
      String output = "";

      Employee employee;  // superclass reference

      Boss boss = new Boss( "John", "Smith", 800.0 );

      CommissionWorker commissionWorker =
         new CommissionWorker( 
            "Sue", "Jones", 400.0, 3.0, 150 );

      PieceWorker pieceWorker =
         new PieceWorker( "Bob", "Lewis", 2.5, 200 );

      HourlyWorker hourlyWorker =
         new HourlyWorker( "Karen", "Price", 13.75, 40 );

      DecimalFormat precision2 = new DecimalFormat( "0.00" );

      // Employee reference to a Boss 
      employee = boss;  

      output += employee.toString() + " earned $" +
         precision2.format( employee.earnings() ) + "\n" +
         boss.toString() + " earned $" +
         precision2.format( boss.earnings() ) + "\n";

      // Employee reference to a CommissionWorker
      employee = commissionWorker;

      output += employee.toString() + " earned $" +
         precision2.format( employee.earnings() ) + "\n" +
         commissionWorker.toString() + " earned $" +
         precision2.format( 
            commissionWorker.earnings() ) + "\n";

      // Employee reference to a PieceWorker
      employee = pieceWorker;
  
      output += employee.toString() + " earned $" +
         precision2.format( employee.earnings() ) + "\n" +
         pieceWorker.toString() + " earned $" +
         precision2.format( pieceWorker.earnings() ) + "\n";
   
      // Employee reference to an HourlyWorker
      employee = hourlyWorker;  

      output += employee.toString() + " earned $" +
         precision2.format( employee.earnings() ) + "\n" +
         hourlyWorker.toString() + " earned $" +
         precision2.format( hourlyWorker.earnings() ) + "\n";

      ta = new TextArea(output,10,50);
      add(ta);
   }
}