Inheritance - Absolute Java - page 466

We need to make our definition work for any kind of object. If the object is not
an Employee , we simply return false . The calling object is an Employee , so if the
argument is not an Employee , they should not be considered equal. But how can we
tell whether the parameter is or is not of type Employee ?
Every object inherits the method getClass() from the class Object . The method
getClass() is marked final in the class Object , so it cannot be overridden. For any
object o , o.getClass() returns a representation of the class used to create o . For example,
after the following is executed,

o = new Employee();
o.getClass() returns a representation Employee .
We will not describe the details of this representation except to say that two
such representations should be compared with == or != if you want to know if
two representations are the same. Thus,

if (object1.getClass() == object2.getClass())
System.out.println("Same class.");
else
System.out.println("Not the same class.");
will output "Same class." if object1 and object2 were created with the same class
when they were created using new , and output "Not the same class." otherwise.
Our final version of the method equals is shown in Display 7.10 . Note that we
have also taken care of one more possible case. The predefined constant null can
be plugged in for a parameter of type Object . The Java documentation says that an
equals method should return false when comparing an object and the value null .
So that is what we have done.
On the accompanying website, the subdirectory improvedEquals (of the directory
for this chapter) has a definition of the class Employee that includes this definition
of equals .

extra code
on website

Display 7.10 A Better equals Method for the Class Employee

1 public boolean equals(Object otherObject)

2 {

3 if (otherObject == null )

4

return false;

5

else if (getClass() != otherObject.getClass())

6 return false;

7 else

8 {

9 Employee otherEmployee = (Employee)otherObject;

10 return (name.equals(otherEmployee.name)
11 && hireDate.equals(otherEmployee.hireDate));

12 }

13 }