Polymorphism

Checked with version: 4.1

-

Difficulty: Intermediate

How to use Polymorphism, Upcasting, and Downcasting to create powerful and dynamic functionality between inherited classes.

Polymorphism

Intermediate Scripting

Fruit Class

Code snippet

using UnityEngine;
using System.Collections;

public class Fruit 
{
    public Fruit()
    {
        Debug.Log("1st Fruit Constructor Called");
    }
    
    public void Chop()
    {
        Debug.Log("The fruit has been chopped.");     
    }
    
    public void SayHello()
    {
        Debug.Log("Hello, I am a fruit.");
    }
}
#pragma strict

public class Fruit 
{
    public function Fruit ()
    {
        Debug.Log("1st Fruit Constructor Called");
    }
    
    public function Chop ()
    {
        Debug.Log("The fruit has been chopped.");     
    }
    
    public function SayHello ()
    {
        Debug.Log("Hello, I am a fruit.");
    }
}
import UnityEngine
import System.Collections


public class Fruit:

    
    public def constructor():
        Debug.Log('1st Fruit Constructor Called')

    
    public def Chop():
        Debug.Log('The fruit has been chopped.')

    
    public def SayHello():
        Debug.Log('Hello, I am a fruit.')

Apple Class

Code snippet

using UnityEngine;
using System.Collections;

public class Apple : Fruit 
{
    public Apple()
    {
        Debug.Log("1st Apple Constructor Called");
    }
    
    //Apple has its own version of Chop() and SayHello(). 
    //When running the scripts, notice when Fruit's version
    //of these methods are called and when Apple's version
    //of these methods are called.
    //In this example, the "new" keyword is used to supress
    //warnings from Unity while not overriding the methods
    //in the Apple class.
    public new void Chop()
    {
        Debug.Log("The apple has been chopped.");     
    }
    
    public new void SayHello()
    {
        Debug.Log("Hello, I am an apple.");
    }
}
#pragma strict

public class Apple extends Fruit 
{
    public function Apple ()
    {
        Debug.Log("1st Apple Constructor Called");
    }
    
    //Apple has its own version of Chop() and SayHello(). 
    //When running the scripts, notice when Fruit's version
    //of these methods are called and when Apple's version
    //of these methods are called.
    //In this example, the "new" keyword is used to supress
    //warnings from Unity while not overriding the methods
    //in the Apple class.
    public function Chop ()
    {
        Debug.Log("The apple has been chopped.");     
    }
    
    public function SayHello ()
    {
        Debug.Log("Hello, I am an apple.");
    }
}
import UnityEngine
import System.Collections


public class Apple(Fruit):

    public def constructor():
        Debug.Log('1st Apple Constructor Called')

    
    //Apple has its own version of Chop() and SayHello(). 
    //When running the scripts, notice when Fruit's version
    //of these methods are called and when Apple's version
    //of these methods are called.
    //In this example, the "new" keyword is used to supress
    //warnings from Unity while not overriding the methods
    //in the Apple class.
    public new def Chop():
        Debug.Log('The apple has been chopped.')

    
    public new def SayHello():
        Debug.Log('Hello, I am an apple.')

FruitSalad Class

Code snippet

using UnityEngine;
using System.Collections;

public class FruitSalad : MonoBehaviour
{
    void Start () 
    {
        //Notice here how the variable "myFruit" is of type
        //Fruit but is being assigned a reference to an Apple. This
        //works because of Polymorphism. Since an Apple is a Fruit,
        //this works just fine. While the Apple reference is stored
        //in a Fruit variable, it can only be used like a Fruit
        Fruit myFruit = new Apple();

        myFruit.SayHello();
        myFruit.Chop();
        
        //This is called downcasting. The variable "myFruit" which is 
        //of type Fruit, actually contains a reference to an Apple. Therefore,
        //it can safely be turned back into an Apple variable. This allows
        //it to be used like an Apple, where before it could only be used
        //like a Fruit.
        Apple myApple = (Apple)myFruit;
        
        myApple.SayHello();
        myApple.Chop(); 
    }
}
#pragma strict

function Start () 
{
    //Notice here how the variable "myFruit" is of type
    //Fruit but is being assigned a reference to an Apple. This
    //works because of Polymorphism. Since an Apple is a Fruit,
    //this works just fine. While the Apple reference is stored
    //in a Fruit variable, it can only be used like a Fruit
    var myFruit = new Apple();

    myFruit.SayHello();
    myFruit.Chop();
    
    //This is called downcasting. The variable "myFruit" which is 
    //of type Fruit, actually contains a reference to an Apple. Therefore,
    //it can safely be turned back into an Apple variable. This allows
    //it to be used like an Apple, where before it could only be used
    //like a Fruit.
    var myApple = myFruit as Apple;
    
    myApple.SayHello();
    myApple.Chop(); 
}
import UnityEngine
import System.Collections


public class FruitSalad(MonoBehaviour):

    
    private def Start():
        //Notice here how the variable "myFruit" is of type
        //Fruit but is being assigned a reference to an Apple. This
        //works because of Polymorphism. Since an Apple is a Fruit,
        //this works just fine. While the Apple reference is stored
        //in a Fruit variable, it can only be used like a Fruit
        myFruit as Fruit = Apple()
        
        myFruit.SayHello()
        myFruit.Chop()
        
        //This is called downcasting. The variable "myFruit" which is 
        //of type Fruit, actually contains a reference to an Apple. Therefore,
        //it can safely be turned back into an Apple variable. This allows
        //it to be used like an Apple, where before it could only be used
        //like a Fruit.
        myApple = (myFruit cast Apple)
        
        myApple.SayHello()
        myApple.Chop()

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