Tutorials : The Pitfalls of Inheritance :

Restricting inheritance…

Sometimes in your design you would like to stop some classes and methods being inherited. The final keyword in Java achieves this functionality. When you declare a class to be final, no other sub class of it can be created. Similarly, when you declare a method to be final, no sub class can override that method.

Overriding member variables…

So far we have talked about how can you override the methods declared in the super class. It is also possible to hide the member variables declared in the super class, by declaring a member variable in the sub class with the same name as in super class. The type of the field does not matter, only the name needs to match. Notice that when you hide a member variable in the sub class, you can still access the super class variable by using the super keyword. This means that the member variables cannot be overridden but can only be hidden. It is important to notice this subtle distinction between overriding and hiding.

The logic behind that Java allows the hiding of member variables, is that you can then create a sub class of any super class without detailed knowledge of its internal implementation. This is more in the line of encapsulation.

How it works…

Object Initialization and Inheritance

public class Vehicle

{

   private String registration;

    

   public void accelarate()

   {

 

   }

   public void stop()

   {

       //stop the engine

 

   }

}

 

 

public class Car extends Vehicle

{

    private String model;

 

    public Car()

    {

 

    }

 

    public void stop()

    {

        //stop the engine

        //lock the steering wheel

    }

 

    public void switchOnWiper()

    {

 

    }

 

 

}

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