Modifying the Super Class Behavior…
With inheritance mechanism, although the sub class by default
inherits all the interfaces and implementations of the super
class, it is possible to override any of the implementations in
the sub class. It is also perfectly possible to extend the
interfaces by adding new methods to the sub class. Both of these
are mechanisms to modify or extend the functionality of the
super class. For example, consider the following inheritance
scenario in Listing 1.
public class Vehicle
{
public void stop()
{
//stop the engine
}
public void accelarate()
{
}
}
public class Car extends Vehicle
{
public Car()
{
}
public void stop()
{
//stop the engine
//lock the steering wheel
}
public void switchOnWiper()
{
}
}
Listing 1: The Vehicle-Car interface inheritance
In this example, we have modelled Car IS A Vehicle. The Car
class overrides the stop() method implementation of its
super class Vehicle. However, it decides to reuse the
accelarate() implementation from its super class.
As a result of this inheritance relationship, we will be able
to write a VehicleTester class in the following form.
public class VehicleTester
{
public void testVehicle(Vehicle vechicle)
{
//test the accelarate behaviour
vechicle.accelarate();
//test the stop behaviour
vechicle.stop();
}
}
Listing 2. The example benefits of using inheritance relationship
In this example, you can immediately see the benefits of
inheritance relationship. We could write a single method
accepting a super class type and we are able to pass any sub
class to the same method. This greatly reduces the strongly
typed nature of code and increases the flexibility of the
application module.
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