Overriding

Fruit Class

using UnityEngine;
using System.Collections;

public class Fruit 
{
    public Fruit ()
    {
        Debug.Log("1st Fruit Constructor Called");
    }

    //These methods are virtual and thus can be overriden
    //in child classes
    public virtual void Chop ()
    {
        Debug.Log("The fruit has been chopped.");        
    }

    public virtual void SayHello ()
    {
        Debug.Log("Hello, I am a fruit.");
    }
}

Apple Class

using UnityEngine;
using System.Collections;

public class Apple : Fruit 
{
    public Apple ()
    {
        Debug.Log("1st Apple Constructor Called");
    }

    //These methods are overrides and therefore
    //can override any virtual methods in the parent
    //class.
    public override void Chop ()
    {
        base.Chop();
        Debug.Log("The apple has been chopped.");        
    }

    public override void SayHello ()
    {
        base.SayHello();
        Debug.Log("Hello, I am an apple.");
    }
}

FruitSalad Class

using UnityEngine;
using System.Collections;

public class FruitSalad : MonoBehaviour 
{    
    void Start () 
    {
        Apple myApple = new Apple();

        //Notice that the Apple version of the methods
        //override the fruit versions. Also notice that
        //since the Apple versions call the Fruit version with
        //the "base" keyword, both are called.
        myApple.SayHello();
        myApple.Chop();    

        //Overriding is also useful in a polymorphic situation.
        //Since the methods of the Fruit class are "virtual" and
        //the methods of the Apple class are "override", when we 
        //upcast an Apple into a Fruit, the Apple version of the 
        //Methods are used.
        Fruit myFruit = new Apple();
        myFruit.SayHello();
        myFruit.Chop();
    }
}