// Fig. 10.12: Employee.java
// Employee abstract superclass.

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

  // constructor
  public Employee( String first, String last, String ssn )
  {
    firstName = first;
    lastName = last;
    socialSecurityNumber = ssn;
  }

  // set first name
  public void setFirstName( String first )
  {
    firstName = first;
  }
  // return first name
  public String getFirstName()
  {
    return firstName;
  }

  // set last name
  public void setLastName( String last )
  {
    lastName = last;
  }

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

  // set social security number
  public void setSocialSecurityNumber( String number )
  {
    socialSecurityNumber = number;  // should validate
  }

  // return social security number
  public String getSocialSecurityNumber()
  {
    return socialSecurityNumber;
  }

  // return String representation of Employee object
  public String toString()
  {
    return getFirstName() + " " + getLastName() +
        "\nsocial security number: " + getSocialSecurityNumber();
  }

  // abstract method overridden by subclasses
  public abstract double earnings();

} // end abstract class Employee