What is polymorphism, what is it for, and how is i

Question

I was watching a Google Tech Talks video, and they frequently referred to polymorphism.

What is polymorphism, what is it for, and how is it used?

Answer 1

Polymorphism allows the same routine (function, method) to act on different types.

Since many existing answers are conflating subtyping with polymorphism, here are three ways (including subtyping) to implement polymorphism.

• Parameteric (generic) polymorphism allows a routine to accept one or more type parameters, in addition to normal parameters, and runs itself on those types.
• Subtype polymorphism allows a routine to act on any subtype of its parameters.
• Ad hoc polymorphism generally uses routine overloading to grant polymorphic behavior, but can refer to other polymorphism implementations too.

See also:

http://wiki.c2.com/?CategoryPolymorphism

https://en.wikipedia.org/wiki/Polymorphism_(computer_science)

Answer 2

(I was browsing another article on something entirely different.. and polymorphism popped up... Now I thought that I knew what Polymorphism was.... but apparently not in this beautiful way explained.. Wanted to write it down somewhere.. better still will share it... )

http://www.eioba.com/a/1htn/how-i-explained-rest-to-my-wife

read on from this part:

..... polymorphism. That's a geeky way of saying that different nouns can have the same verb applied to them.

Answer 3

In Object Oriented languages, polymorphism allows treatment and handling of different data types through the same interface. For example, consider inheritance in C++: Class B is derived from Class A. A pointer of type A* (pointer to class A) may be used to handle both an object of class A AND an object of class B.

Answer 4

If you think about the Greek roots of the term, it should become obvious.

• Poly = many: polygon = many-sided, polystyrene = many styrenes ^(a), polyglot = many languages, and so on.
• Morph = change or form: morphology = study of biological form, Morpheus = the Greek god of dreams able to take any form.

So polymorphism is the ability (in programming) to present the same interface for differing underlying forms (data types).

For example, in many languages, integers and floats are implicitly polymorphic since you can add, subtract, multiply and so on, irrespective of the fact that the types are different. They're rarely considered as objects in the usual term.

But, in that same way, a class like BigDecimal or Rational or Imaginary can also provide those operations, even though they operate on different data types.

The classic example is the Shape class and all the classes that can inherit from it (square, circle, dodecahedron, irregular polygon, splat and so on).

With polymorphism, each of these classes will have different underlying data. A point shape needs only two co-ordinates (assuming it's in a two-dimensional space of course). A circle needs a center and radius. A square or rectangle needs two co-ordinates for the top left and bottom right corners and (possibly) a rotation. An irregular polygon needs a series of lines.

By making the class responsible for its code as well as its data, you can achieve polymorphism. In this example, every class would have its own Draw() function and the client code could simply do:

shape.Draw()

to get the correct behavior for any shape.

This is in contrast to the old way of doing things in which the code was separate from the data, and you would have had functions such as drawSquare() and drawCircle().

Object orientation, polymorphism and inheritance are all closely-related concepts and they're vital to know. There have been many "silver bullets" during my long career which basically just fizzled out but the OO paradigm has turned out to be a good one. Learn it, understand it, love it - you'll be glad you did :-)

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^(a) I originally wrote that as a joke but it turned out to be correct and, therefore, not that funny. The momomer styrene happens to be made from carbon and hydrogen, C8H8, and polystyrene is made from groups of that, (C8H8)n.

Perhaps I should have stated that a polyp was many occurrences of the letter p although, now that I've had to explain the joke, even that doesn't seem funny either.

Sometimes, you should just quit while you're behind :-)

Answer 5

Polymorphism is an ability of object which can be taken in many forms. For example in human class a man can act in many forms when we talk about relationships. EX: A man is a father to his son and he is husband to his wife and he is teacher to his students.

Answer 6

The term polymorphism comes from:

poly = many

morphism = the ability to change

In programming, polymorphism is a "technique" that lets you "look" at an object as being more than one type of thing. For instance:

A student object is also a person object. If you "look" (ie cast) at the student, you can probably ask for the student ID. You can't always do that with a person, right? (a person is not necessarily a student, thus might not have a student ID). However, a person probably has a name. A student does too.

Bottom line, "looking" at the same object from different "angles" can give you different "perspectives" (ie different properties or methods)

So this technique lets you build stuff that can be "looked" at from different angles.

Why do we use polymorphism? For starters ... abstraction. At this point it should be enough info :)