The class Worker is defined below. The class includes the method getEarnings, which is intended to return the total amount earned by the worker.

public class Worker

$\{$

private double hourlyRate;

private double hoursWorked;

private double earnings;

public Worker$($double rate, double hours$)$

$\{$

hourlyRate $=$ rate;

hoursWorked $=$ hours;

$\}$

private void calculateEarnings$()$

$\{$

double earnings $=0\mathrm{.}0$;

earnings $+=$ hourlyRate $*$ hoursWorked;

$\}$

public double getEarnings$()$

$\{$

calculateEarnings$()$;

return earnings;

$\}$

$\}$

The following code segment appears in a method in a class other than Worker. The code segment is intended to print the value $800\mathrm{.}0,$ but instead prints a different value because of an error in the Worker class. Worker bob $=$ new Worker$(20\mathrm{.}0,40\mathrm{.}0)$;

System.out.println$($bob$.$getEarnings$())$;

Which of the following best explains why an incorrect value is printed?