Fixing Employee.equals

• Violates two rules
• Add test for null:
  if (otherObject == null) return false
• What happens if otherObject not an Employee
• Should return false (because of symmetry)
• Common error: use of instanceof
  if (!(otherObject instanceof Employee)) return false;
     // don't do this for non-final classes
  
• Violates symmetry: Suppose e, m have same name, salary
  e.equals(m) is true (because m instanceof Employee)
  m.equals(e) is false (because e isn't an instance of Manager)
• Remedy: Test for class equality
  if (getClass() != otherObject.getClass()) return false;