cannot understand the point of downcasting in the following code

how are you?
wanted to ask you why this code is using Downcasting (1st code fragment line 36-37)? i.e.
in the line below

should not the compiler dynamically 'find out' that it is dealing with a subclass of CurrentEmployee
and use the appropriate functions in that sub-class (BasePlusCommissionEmployee)?
thank you

=================

// Fig. 10.17: PayrollSystemTest.java
// Employee hierarchy test program.
import java.text.DecimalFormat;
import javax.swing.JOptionPane;

public class PayrollSystemTest {

public static void main( String[] args ) 
   {
      DecimalFormat twoDigits = new DecimalFormat( "0.00" );

// create Employee array
      Employee employees[] = new Employee[ 4 ];

// initialize array with Employees
      employees[ 0 ] = new SalariedEmployee( "John", "Smith", 
         "111-11-1111", 800.00 );
      employees[ 1 ] = new CommissionEmployee( "Sue", "Jones", 
         "222-22-2222", 10000, .06 );
      employees[ 2 ] = new BasePlusCommissionEmployee( "Bob", "Lewis", 
         "333-33-3333", 5000, .04, 300 );
      employees[ 3 ] = new HourlyEmployee( "Karen", "Price", 
         "444-44-4444", 16.75, 40 );

String output = "";

// generically process each element in array employees
      for ( int i = 0; i < employees.length; i++ ) {
         output += employees[ i ].toString();

// determine whether element is a BasePlusCommissionEmployee
         if ( employees[ i ] instanceof BasePlusCommissionEmployee ) {

// downcast Employee reference to 
            // BasePlusCommissionEmployee reference
            BasePlusCommissionEmployee currentEmployee = 
               ( BasePlusCommissionEmployee ) employees[ i ];

double oldBaseSalary = currentEmployee.getBaseSalary();
            output += "\nold base salary: $" + oldBaseSalary;      
            
            currentEmployee.setBaseSalary( 1.10 * oldBaseSalary );
            output += "\nnew base salary with 10% increase is: $" +
               currentEmployee.getBaseSalary();

} // end if

output += "\nearned $" + employees[ i ].earnings() + "\n";

} // end for

// get type name of each object in employees array
      for ( int j = 0; j < employees.length; j++ )
         output += "\nEmployee " + j + " is a " +
            employees[ j ].getClass().getName();

JOptionPane.showMessageDialog( null, output );  // display output
      System.exit( 0 );

} // end main

} // end class PayrollSystemTest

==============
BasePlusCommissionEmployee
==============

public class BasePlusCommissionEmployee extends CommissionEmployee {
   private double baseSalary;  // base salary per week

// constructor
   public BasePlusCommissionEmployee( String first, String last, 
      String socialSecurityNumber, double grossSalesAmount,
      double rate, double baseSalaryAmount )
   {
      super( first, last, socialSecurityNumber, grossSalesAmount, rate );
      setBaseSalary( baseSalaryAmount );
   }

// set base-salaried commission employee's base salary
   public void setBaseSalary( double salary )
   {
      baseSalary = salary < 0.0 ? 0.0 : salary;
   }

// return base-salaried commission employee's base salary
   public double getBaseSalary()
   {
      return baseSalary;
   }

// calculate base-salaried commission employee's earnings;
   // override method earnings in CommissionEmployee
   public double earnings()
   {
      return getBaseSalary() + super.earnings();
   }

// return String representation of BasePlusCommissionEmployee
   public String toString()
   {
      return "\nbase-salaried commission employee: " +
         super.getFirstName() + " " + super.getLastName() +
         "\nsocial security number: " + super.getSocialSecurityNumber();
   } 
   
} // end class BasePlusCommissionEmployee

============
CommissionEmployee
=============

// Fig. 10.15: CommissionEmployee.java
// CommissionEmployee class extends Employee.

public class CommissionEmployee extends Employee {
   private double grossSales;      // gross weekly sales
   private double commissionRate;  // commission percentage

// constructor
   public CommissionEmployee( String first, String last, 
      String socialSecurityNumber, 
      double grossWeeklySales, double percent )
   {
      super( first, last, socialSecurityNumber );
      setGrossSales( grossWeeklySales );
      setCommissionRate( percent );
   }

// set commission employee's rate
   public void setCommissionRate( double rate )
   {
      commissionRate = ( rate > 0.0 && rate < 1.0 ) ? rate : 0.0;
   }

// return commission employee's rate
   public double getCommissionRate()
   {
      return commissionRate;
   }

// set commission employee's weekly base salary
   public void setGrossSales( double sales )
   {
      grossSales = sales < 0.0 ? 0.0 : sales;
   }

// return commission employee's gross sales amount
   public double getGrossSales()
   {
      return grossSales;
   }

// calculate commission employee's pay;
   // override abstract method earnings in Employee
   public double earnings()
   {
      return getCommissionRate() * getGrossSales();
   }

// return String representation of CommissionEmployee object
   public String toString()
   {
      return "\ncommission employee: " + super.toString();
   } 
   
} // end class CommissionEmployee

You usually do it to call methods that a class has, but that its interface/super class has not. Methods getBaseSalary and setBaseSalary are called. Are these methods also in Employee ?

Christophe Verré wrote:You usually do it to call methods that a class has, but that its interface/super class has not. Methods getBaseSalary and setBaseSalary are called. Are these methods also in Employee ?

yes, i believe they are in the Employee class

Is that example from Deitel and Deitel? It looks familiar.

I agree that if you are not using any specific Commission methods, the cast is unnecessary.

But it's inside an instanceof, so there must be a reason, no? And if there isn't, wow.

yes it is from Deitel and Deitel book (5th edition)

Get a newer edition than 5th. Get 6th or newer, which describe the new features in Java 5.

I had a quick look through my 6th edition Deitel and can't see that cast. Which example number is it in your edition?