Question

My relative is studying programming and has a hard time understanding classes. He has trouble understanding for example that you need to instantiate it, that methods cannot access variables in other methods and if you change a variable in one instance of a class it doesn’t change for other instances.

I’ve tried to use analogies like a class definition is like a blueprint of a house. And instances are houses made from that blueprint.

How do you explain classes and OO in general?

Answer 1

Seriously use Animals, it works great. And that’s what nailed the concept for me years ago. Just found this C# code. It seems good

    // Assembly: Common Classes     // Namespace: CommonClasses      public interface IAnimal     {         string Name         {               get;          }         string Talk();     }      // Assembly: Animals     // Namespace: Animals      public class AnimalBase     {         private string _name;         AnimalBase(string name)         {            _name = name;         }         public string Name         {            get            {               return _name;            }         }     }      // Assembly: Animals     // Namespace: Animals      public class Cat : AnimalBase, IAnimal     {         public Cat(String name) :             base(name)         {         }          public string Talk() {             return 'Meowww!';         }     }      // Assembly: Animals     // Namespace: Animals      public class Dog : AnimalBase, IAnimal     {         public Dog(string name) :              base(name)         {         }          public string Talk() {             return 'Arf! Arf!';         }     }      // Assembly: Program     // Namespace: Program     // References and Uses Assemblies: Common Classes, Animals      public class TestAnimals     {         // prints the following:         //         // Missy: Meowww!         // Mr. Bojangles: Meowww!         // Lassie: Arf! Arf!         //         public static void Main(String[] args)         {             List<IAnimal> animals = new List<IAnimal>();             animals.Add(new Cat('Missy'));             animals.Add(new Cat('Mr. Bojangles'));             animals.Add(new Dog('Lassie'));              foreach(IAnimal animal in animals)             {                  Console.WriteLine(animal.Name + ': ' + animal.Talk());             }             }     } 

And once he’s got this nailed, you challenge him to define Bird (fly), and then Penguin (fly!?)