Inheritance

Definition

Inheritance is the process by which code applying to a given class can be functionally reused by another class with minimal effort. S.N. any Class which inherits from another class possesses an 'IS A' relationship (counter to a 'HAS A' relationship). Inheritance is best explained via abstraction, for example if we abstract a Ferret into it's many sub components, we find a Ferret 'IS A' Mamal which 'IS A' Animal. Class abstraction can have numerous degrees of seperation and allows the implementation of inheritance functionality, namely allowing any class in the inheritance chain to become a parent to a new class; for example if we add another mamal to the chain such as tiger, we can have this new class inherit all the functionality of the class Mamal and allow it to posess the exact same base to define itself as we did for Feret.

Inheritance Example

To display the qualities &amp additional functionality available to a program which implements inheritance, we will create a short program displaying Animals.

 1 private enum EGender {
 2   Male, female
 3   // Enumeration containing
 4 }; // possible gender values
 5 
 6 class Animal {
 7     public Animal(name, age, gender) {
 8         this.name = name; 
 9         this.age = age;
10         this.gender = gender;
11     }
12 
13     public void Walk() {
14         Console.WriteLine("{0} Is a {1} & is {2} Years Old",
15             this.name, this.gender, this.age)
16     }
17 
18     private int _age;
19     private String _name;
20     private EGender _gender;
21 
22     public int age { get { return _age; } set { _age = value; } }
23     public String name { get { return _name; } set { _name = value; } }
24     public EGender gender { get { return _gender; } set { _gender = value; } }
25 }

• A new Mammal class that inherits all aspect of the Animal class e.g name or gender but also adds its own unique

data type, hairColour. This data is not accessible to any objects created from the Animal class.

• Another thing inheritance allows you to do is override existing functions or data types. e.g.

in the Mammal class, the inherited function Walk() is being overridden meaning it can do something completely different to what it does in the Animal class. This is called polymorphism

 
Class Mammal: Animal{
   private enum hairColour{
      White,
      Black,
      Brown,
      Other
   };
   public Mammal(){ //Class Constructor
      //some code to run when a new instance of the class is created
   }
   public override void Walk(){
      //Some different code
   }
   public enum HairColour{
      get{ return hairColour; }
      set{ hairColour = value; }
   }
}

For examples on how inheritance can be used to psuedo link different object instances to a given global class (allowing different, for example, Animals to all be contained in a single array despite being different types) view the examples on Arrays at http://compsci.duckdns.org/mediawiki/index.php/Arrays.