Week 5: Class hierarchies/07A. Overwrite and override [Overwrite - METHOD, PARAMS]

An essential part of specialisation in the child classes is the MODIFICATION of the FUNCTIONALITY inherited from the parent class. 
In other words, a child class can either ADD completely new features or MODIFY inherited features.

Implementing an inherited method in a new child class is called OVERWRITING the method.

To overwrite a method, it is sufficient to implement the corresponding method in the inherited class. 
In this case, the objects created from the inherited class will automatically use the 'newer' implementation. 
The method to be overwritten must therefore have 
- the SAME NAME as the original method, and
- the same list of PARAMETERS as the original method. 


The NUMBER, TYPE and ORDER of PARAMETERS must therefore be exactly the same. 
The name of the formal parameters is irrelevant in this context.

As a simple example, consider the class Dog with the method bark:
class Dog {
    public void bark() {
        System.out.println("Bark!");
    }
}
 

Let's then write a child class of the Dog class BigDog, with a reimplemented or overwritten barking method:
class BigDog extends Dog {
    public void bark() {
        System.out.println("WOOF WOOF!");
    }
}
 

The version of the method used now depends on the type of object being created:
public static void main(String[] args) {
    Random r = new Random();
    
    Dog snoopy = new Dog();
    BigDog cerberus = new BigDog();
    
    snoopy.bark();
    cerberus.bark();
}
 

Program outputs:
Bark!
WOOF WOOF!