Horstmann Chapter 7

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;