Try to describe polymorphism as easy as you can

Question

we can find a lot of information about the subject on the internet and books

http://en.wikipedia.org/wiki/Type_polymorphism

but lets try to make it as simple as we can .

Answer 1

The way I try and think of it is something that looks the same but can have different functionality depending on the instance. So you can have a type

interface IJobLoader

but depending on how it is used can have different functionality while still looking the same. You may have instances for BatchJobLoader, NightlyJobLoader etc

Maybe I am way off.

Answer 2

The Actor vs. the Character (or Role)

Answer 3

This is from my answer from a similiar question. Here's an example of polymorphism in pseudo-C#/Java:

class Animal
{
    abstract string MakeNoise ();
}

class Cat : Animal {
    string MakeNoise () {
        return "Meow";
    }
}

class Dog : Animal {
    string MakeNoise () {
        return "Bark";
    }
}

Main () {
   Animal animal = Zoo.GetAnimal ();
   Console.WriteLine (animal.MakeNoise ());
}

The Main() method doesn't know the type of the animal and depends on a particular implementation's behavior of the MakeNoise() method.

Answer 4

This is a better article actually

Polymorphism allows Objects to "Look" the same, but behave in different ways. The usual example is to take an animal base class with a Speak() Method, A dog subclass would emit a Bark whereas a Pig subclass would emit an oink.

The 5 second short answer most people use so other developers can get their head around Polymorphism is overloading and overriding

Answer 5

two objects respond to the same message with different behaviors; the caller doesn't have to care

Answer 6

If it walks like a duck and quacks like a duck, then you can treat it as a duck anywhere you need a duck.

Answer 7

The simplest description of polymorphism is that it is a way to reduce if/switch statements.

It also has the benefit of allowing you to extend your if/switch statements (or other people's ones) without modifying existing classes.

For example consider the Stream class in .NET. Without polymorphism it would be a single massive class where each method implements a switch statement something like:

public class Stream
{
    public int Read(byte[] buffer, int offset, int count)
    {
        if (this.mode == "file")
        {
            // behave like a file stream
        }
        else if (this.mode == "network")
        {
            // behave like a network stream
        }
        else // etc.
    }
}

Instead we allow the runtime to do the switching for us in a more efficient way, by automatically choosing the implementation based on the concrete type (FileStream, NetworkStream), e.g.

public class FileStream : Stream
{
    public override int Read(byte[] buffer, int offset, int count)
    {
        // behave like a file stream
    }
}

public class NetworkStream : Stream
{
    public override int Read(byte[] buffer, int offset, int count)
    {
        // behave like a network stream
    }
}

Answer 8

You have two houses with driveways, you can park your car in either driveway, but only one of them has the hot housewife.

Your car doesn't care either way.

Answer 9

Poly: many
Morphism: forms / shapes

Answer 10

Simplest way to describe it: a verb that can apply to more than one kind of object.

Everything else, as Hillel said, is just commentary.

Answer 11

Polymorphism is treating things abstractly by relying on knowledge of a common "parent" (think heirarchies like Animal as a parent of Dogs and Cats).

For example, all Animals can breathe oxygen, and while they may each do this differently you could design a facility that provides oxygen for Animals to breathe, supporting both Dogs and Cats.

As a little extra, you can do this even though Animal is an "abstract" identifier (there is no real "Animal" thing, just types of Animals).

Answer 12

Polymorphism is the storing of values of more than one type in a location of a single type.

Note that most of the other answers to this question, at the time of my writing, are actually describing dynamic dispatch, not polymorphism.

Dynamic dispatch requires polymorphism, but the reverse is not true. One could imagine a language very similar to Java or C# but whose System.Object had no members; typecasting would be necessary before doing anything with the value. In this notional language, there would be polymorphism, but not necessarily virtual methods, or any other dynamic dispatch mechanisms.

Dynamic dispatch is the related but distinct concept, well enough described in most of the other answers. However, the way it normally works in object-oriented languages (selecting a function based on the first ('this' or 'Self') argument type) is not the only way it can work. Multiple dispatch is also possible, where the selection is applied across the types of all the arguments.

Similarly, overload resolution and multiple dispatch are exact analogues of one another; overload resolution is multiple dispatch applied to static types, while multiple dispatch is overload resolution applied to runtime types stored in polymorphic locations.

Answer 13

The term polymorphism can also apply to overloading functions. For example,

string MyFunc(ClassA anA);
string MyFunc(ClassB aB);

is a non-object oriented example of polymorphism.

Answer 14

It is a way to treat different things that can do something something similar in the same way without caring how they do it.

Let's say you have a game with a bunch of different types of Vehicles driving around such as Car, Truck, Skateboard, Airplane, etc... They all can Stop, but each Vehicle stops in a different way. Some Vehicles may need to shift down gears, and some may be able to come to a cold stop. Polymophism lets you do this

foreach (Vehicle v in Game.Vehicles)
{
   v.Stop();
}

The way that stop is implemented is deferred to the different Vehicles so your program doesn't have to care about it.

Answer 15

Is the ability that objects have to respond to the same message in different ways.

For instance , in languages such as smalltalk, Ruby, Objective-C, you just have to send the message and they will respond.

 dao  = XmlDao.createNewInstance()    #obj 1
 dao.save( data )

 dao = RdbDao.createNewnewInstance()  #obj 2
 dao.save( data )

In this example two different objects, responded in different ways to the same messages: "createNewInstance() and save( obj )"

They act in different ways, to the same message. In the above languages, the classes might not even be in the same class hierarchy, it is enough that they respond to the message.

In languages such as Java, C++, C# etc. In order to assign the object to an object reference, they must share the same type hierarchy either by implementing the interface or by being subclass of a common class.

easy .. and simple.

Polymorphism is by far, the most important and relevant feature of object oriented programming.

Answer 16

Interact as you know, accept the response.

Answer 17

Polymorphism is what you get when the same method applies to multiple classes. For example, both a String and a List might have "Reverse" methods. Both methods have the same name ("Reverse"). Both methods do something very similar (reverse all the characters or reverse the order of the elements in the list). But the implementation of each "Reverse" method is different and specific to its class. (In other words, the String reverses itself like a string, and the List reverses itself like a list.)

To use a metaphor, you could say "Make Dinner" to a French chef or to a Japanese chef. Each would perform "make dinner" in their own characteristic way.

The practical result is that you could create a "Reversing Engine" that accepts an object and calls "Reverse" on it. As long as the object has a Reverse method, your Reversing Engine will work.

To extend the chef analogy, you could build a "Waiterbot" that tells chefs to "Make Dinner". The Waiterbot doesn't have to know what type of dinner is going to be made. It doesn't even have to make sure it's talking to a chef. All that matters is that the "chef" (or fireman, or vending machine, or pet food dispenser) knows what to do when it's told to "Make Dinner".

What this buys you as a programmer is fewer lines of code and either type-safety or late binding. For example here's an example with type safety and early binding (in a c-like language that I'm making up as I go):

class BankAccount {
    void SubtractMonthlyFee
}

class CheckingAccount : BankAccount {}

class SavingsAccount : BankAccount {}

AssessFee(BankAccount acct) {
    // This will work for any class derived from
    //   BankAccount; even classes that don't exist yet
    acct.SubtractMonthlyFee
}

main() {

    CheckingAccount chkAcct;
    SavingsAccount saveAcct;

    // both lines will compile, because both accounts
    //   derive from "BankAccount". If you try to pass in
    //   an object that doesn't, it won't compile, EVEN
    //   if the object has a "SubtractMonthlyFee" method.
    AssessFee(chkAcct);
    AssessFee(saveAcct);
}

Here's an example with no type safety but with late binding:

class DatabaseConnection {
    void ReleaseResources
}

class FileHandle {
    void ReleaseResources
}

FreeMemory(Object obj) {
    // This will work for any class that has a 
    //   "ReleaseResources" method (assuming all
    //   classes are ultimately derived from Object.
    obj.ReleaseResources
}

main() {

    DatabaseConnection dbConn;
    FileHandle fh;

    // You can pass in anything at all and it will
    //   compile just fine. But if you pass in an
    //   object that doesn't have a "ReleaseResources"
    //   method you'll get a run-time error.
    FreeMemory(dbConn);
    FreeMemory(fh);
    FreeMemory(acct); //FAIL! (but not until run-time)
}

For an excellent example, look at the .NET ToString() method. All classes have it because all classes are derived from the Object class. But each class can implement ToString() in a way that makes sense for itself.

EDIT: Simple != short, IMHO

Answer 18

It's just a way to get old cold to call new code. You write some application that accepts some "Shape" interface with methods that others must implement (example - getArea). If someone comes up with a new whiz-bang way to implement that interface your old code can call that new code via the the getArea method.

Answer 19

Polymorphism is the Object Oriented solution to problem of passing a function to another function. In C you can do

 void h() { float x=3.0; printf("%f", x); }
 void k() { int y=5; printf("%i", y); }
 void g(void (*f)()) { f(); }
 g(h);  // output 3.0
 g(k);  // output 5

In C things get complicated if the function depends on additional parameters. If the functions h and k depend on different types of parameters you are in trouble and you must use casting. You have to store those parameters in a data structure, and pass a pointer to that data structure to g which passes it to h or k. h and k cast the pointer into a pointer to the proper structure and unpack the data. Very messy and very unsafe because of possible casting errors:

 void h(void *a) { float* x=(float*)a; printf("%f",*x); }
 void k(void *a) { int* y=(int*)a; printf("%i",*y); }
 void g(void (*f)(void *a),void *a) { f(a); }
 float x=3.0;
 int y=5;
 g(h,&x); // output x
 g(k,&y); // output y

So they invented polymorphism. h and k are promoted to classes and the actual functions to methods, the parameters are member variables of the respective class, h or k. Instead of passing the function around, you pass an instance of the class that contains the function you want. The instance contains its own parameters.

class Base { virtual public void call()=0; }
class H : public Base { float x; public void call() { printf("%f",x);} } h;
class K : public Base { int y; public void call() { printf("%i",y);} } k;
void g(Base &f) { f.call(); };
h.x=3.0;
k.y=5;
g(h); // output h.x
g(k); // output k.x

Answer 20

Same syntax, different semantics.

Answer 21

Polymorphism is dividing the world into boxes based on common properties and treating the items in a given box as interchangeable when you only want to use these common properties.

Answer 22

The ability of an object of some type (e.g. a car) to act (e.g. brake) like one of another type (e.g. a vehicle) which usually suggests common ancestry (e.g. car is a subtype of vehicle) at one point in the type hierarchy.

Answer 23

Polymorphism is the ability to treat different things as if they were the same thing by establishing a shared identity between them then exploiting it.

Answer 24

Apples and oranges are both fruit. Fruit can be eaten. Hence, both apples and oranges can be eaten.

The kicker? You eat them differently! You peel the oranges, but not the apples.

So the implementation differs, but the end result is the same, you eat the fruit.