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

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

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From Understanding and Applying Polymorphism in PHP, Thanks Steve Guidetti.

Polymorphism is a long word for a very simple concept.

Polymorphism describes a pattern in object oriented programming in which classes have different functionality while sharing a common interface.

The beauty of polymorphism is that the code working with the different classes does not need to know which class it is using since they’re all used the same way. A real world analogy for polymorphism is a button. Everyone knows how to use a button: you simply apply pressure to it. What a button “does,” however, depends on what it is connected to and the context in which it is used — but the result does not affect how it is used. If your boss tells you to press a button, you already have all the information needed to perform the task.

In the programming world, polymorphism is used to make applications more modular and extensible. Instead of messy conditional statements describing different courses of action, you create interchangeable objects that you select based on your needs. That is the basic goal of polymorphism.

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Polymorphism in OOP means a class could have different types  inheritance is one way of implementing polymorphism   for example  Shape is an interface  it has Square  Circle  Diamond subtypes  now you have a Square object  you can upcasting Square to Shape automatically  because Square is a Shape  But when you try to downcasting Shape to Square  you must do explicit type casting  because you can t say Shape is Square  it could be Circle as well  so you need manually cast it with code like Square s    Square shape  what if the shape is Circle  you will get java lang ClassCastException  because Circle is not Square

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Usually this refers the the ability for an object of type A to behave like an object of type B  In object oriented programming this is usually achieve by inheritance  Some wikipedia links to read more     Polymorphism in object oriented programming Type polymorphism   EDIT  fixed broken links

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Polymorphism is the ability of the programmer to write methods of the same name that do different things for different types of objects  depending on the needs of those objects   For example  if you were developing a class called Fraction and a class called ComplexNumber  both of these might include a method called display    but each of them would implement that method differently   In PHP  for example  you might implement it like this       Class definitions  class Fraction       public  numerator      public  denominator       public function   construct  n   d                    In real life  you d do some type checking  making sure  d    0  etc           this- gt numerator    n           this- gt denominator    d             public function display                 echo  this- gt numerator          this- gt denominator           class ComplexNumber       public  real      public  imaginary       public function   construct  a   b                 this- gt real    a           this- gt imaginary    b             public function display                 echo  this- gt real          this- gt imaginary    i                 Main program   fraction   new Fraction 1  2    complex   new ComplexNumber 1  2    echo  This is a fraction     fraction- gt display    echo   n    echo  This is a complex number     complex- gt display    echo   n     Outputs   This is a fraction  1 2 This is a complex number  1   2i   Some of the other answers seem to imply that polymorphism is used only in conjunction with inheritance  for example  maybe Fraction and ComplexNumber both implement an abstract class called Number that has a method display    which Fraction and ComplexNumber are then both obligated to implement   But you don t need inheritance to take advantage of polymorphism   At least in dynamically-typed languages like PHP  I don t know about C   or Java   polymorphism allows the developer to call a method without necessarily knowing the type of object ahead of time  and trusting that the correct implementation of the method will be called   For example  say the user chooses the type of Number created    userNumberChoice     GET  userNumberChoice     switch   userNumberChoice        case  fraction            userNumber   new Fraction 1  2           break      case  complex            userNumber   new ComplexNumber 1  2           break     echo  The user s number is      userNumber- gt display    echo   n     In this case  the appropriate display   method will be called  even though the developer can t know ahead of time whether the user will choose a fraction or a complex number

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Generally speaking  it s the ability to interface a number of different types of object using the same or a superficially similar API   There are various forms    Function overloading  defining multiple functions with the same name and different parameter types  such as sqrt float   sqrt double  and sqrt complex    In most languages that allow this  the compiler will automatically select the correct one for the type of argument being passed into it  thus this is compile-time polymorphism  Virtual methods in OOP  a method of a class can have various implementations tailored to the specifics of its subclasses  each of these is said to override the implementation given in the base class   Given an object that may be of the base class or any of its subclasses  the correct implementation is selected on the fly  thus this is run-time polymorphism  Templates  a feature of some OO languages whereby a function  class  etc  can be parameterised by a type   For example  you can define a generic  list  template class  and then instantiate it as  list of integers    list of strings   maybe even  list of lists of strings  or the like   Generally  you write the code once for a data structure of arbitrary element type  and the compiler generates versions of it for the various element types

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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

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Polymorphism literally means  multiple shapes   or many form    Object from different classes and same name method   but workflows are different  A simple example would be   Consider a person X   He is only one person but he acts as many  You may ask how   He is a son to his mother  A friend to his friends  A brother to his sister

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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

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Polymorphism is the ability to use an object in a given class  where all components that make up the object are inherited by subclasses of the given class  This means that once this object is declared by a class  all subclasses below it  and thier subclasses  and so on until you reach the farthest lowest subclass  inherit the object and it s components  makeup    Do remember that each class must be saved in separate files   The following code exemplifies Polymorphism   The SuperClass   public class Parent         Define things that all classes share     String maidenName      String familyTree         Give the top class a default method     public void speak             System out println  We are all Parents              The father  a subclass   public class Father extends Parent        Can use maidenName and familyTree here     String name  Joe       String called  dad          Give the top class a default method     public void speak            System out println  I am   name    the father               The child  another subclass   public class Child extends Father         Can use maidenName  familyTree  called and name here        Give the top class a default method     public void speak            System out println  Hi   called    What are we going to do today               The execution method  references Parent class to start   public class Parenting      public static void main String   args            Parent parents   new Parent            Parent parent   new Father            Parent child   new Child             parents speak            parent speak            child speak              Note that each class needs to be declared in separate   java files  The code should compile  Also notice that you can continually use maidenName and familyTree farther down  That is the concept of polymorphism  The concept of inheritance is also explored here  where one class is can be used or is further defined by a subclass   Hope this helps and makes it clear  I will post the results when I find a computer that I can use to verify the code  Thanks for the patience

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Polymorphism is this   class Cup      int capacity    class TeaCup   Cup      string flavour    class CoffeeCup   Cup      string brand    Cup c   new CoffeeCup     public int measure Cup c        return c capacity     you can pass just a Cup instead of a specific instance  This aids in generality because you don t have to provide a specific measure   instance per each cup type

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Polymorphism is the ability of an object to take on many forms  The most common use of polymorphism in OOP occurs when a parent class reference is used to refer to a child class object  In this example that is written in Java  we have three type of vehicle  We create three different object and try to run their wheels method    public class PolymorphismExample        public static abstract class Vehicle               public int wheels                return 0                       public static class Bike extends Vehicle                Override         public int wheels                         return 2                       public static class Car extends Vehicle                Override         public int wheels                         return 4                       public static class Truck extends Vehicle                Override         public int wheels                         return 18                       public static void main String   args                Vehicle bike   new Bike            Vehicle car   new Car            Vehicle truck   new Truck             System out println  Bike has   bike wheels     wheels            System out println  Car has   car wheels     wheels            System out println  Truck has   truck wheels     wheels               The result is      For more information please visit https   github com m-vahidalizadeh java advanced blob master src files PolymorphismExample java  I hope it helps

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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

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Let s use an analogy  For a given musical script every musician which plays it gives her own touch in the interpretation   Musician can be abstracted with interfaces  genre to which musician belongs can be an abstrac class which defines some global rules of interpretation and every musician who plays can be modeled with a concrete class   If you are a listener of the musical work  you have a reference to the script e g  Bach s  Fuga and Tocata  and every musician who performs it does it polymorphicaly in her own way   This is just an example of a possible design  in Java    public interface Musician     public void play Work work      public interface Work     public String getScript       public class FugaAndToccata implements Work     public String getScript         return Bach getFugaAndToccataScript           public class AnnHalloway implements Musician     public void play Work work           plays in her own style  strict  disciplined     String script   work getScript          public class VictorBorga implements Musician     public void play Work work           goofing while playing with superb style     String script   work getScript          public class Listener     public void main String   args        Musician musician      if  args  null  amp  amp  args length  gt  0  amp  amp  args 0  equals  C            musician   new AnnHalloway          else         musician   new TerryGilliam              musician play new FugaAndToccata

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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  -      a  I originally wrote that as a joke but it turned out to be correct and  therefore  not that funny  The monomer 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  -

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I know this is an older question with a lot of good answers but I d like to include a one sentence answer      Treating a derived type as if it were it s base type    There are plenty of examples above that show this in action  but I feel this is a good concise answer

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In object-oriented programming  polymorphism refers to a programming language s ability to process objects differently depending on their data type or class  More specifically  it is the ability to redefine methods for derived classes

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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

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Polymorphism is the ability to treat a class of object as if it is the parent class   For instance  suppose there is a class called Animal  and a class called Dog that inherits from Animal  Polymorphism is the ability to treat any Dog object as an Animal object like so   Dog  dog   new Dog  Animal  animal   dog

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Polymorphism gives you the ability to create one module calling another  and yet have the compile time dependency point against the flow of control instead of with the flow of control    By using polymorphism  a high level module does not depend on low-level module  Both depend on abstractions  This helps us to apply the dependency inversion principle https   en wikipedia org wiki Dependency inversion principle    This is where I found the above definition  Around 50 minutes into the video the instructor explains the above  https   www youtube com watch v TMuno5RZNeE

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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

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Polymorphism is when you can treat an object as a generic version of something  but when you access it  the code determines which exact type it is and calls the associated code   Here is an example in C   Create four classes within a console application   public abstract class Vehicle       public abstract int Wheels     public class Bicycle   Vehicle       public override int Wheels                 return 2           public class Car   Vehicle       public override int Wheels                 return 4           public class Truck   Vehicle       public override int Wheels                 return 18            Now create the following in the Main   of the module for the console application   public void Main         List lt Vehicle gt  vehicles   new List lt Vehicle gt          vehicles Add new Bicycle         vehicles Add new Car         vehicles Add new Truck          foreach  Vehicle v in vehicles                Console WriteLine              string Format  A  0  has  1  wheels                    v GetType   Name  v Wheels              In this example  we create a list of the base class Vehicle  which does not know about how many wheels each of its sub-classes has  but does know that each sub-class is responsible for knowing how many wheels it has   We then add a Bicycle  Car and Truck to the list   Next  we can loop through each Vehicle in the list  and treat them all identically  however when we access each Vehicles  Wheels  property  the Vehicle class delegates the execution of that code to the relevant sub-class   This code is said to be polymorphic  as the exact code which is executed is determined by the sub-class being referenced at runtime   I hope that this helps you

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Polymorphism    It is the concept of object oriented programming The ability of different objects to respond  each in its own way  to identical messages is called polymorphism   Polymorphism results from the fact that every class lives in its own namespace  The names assigned within a class definition don   t conflict with names assigned anywhere outside it  This is true both of the instance variables in an object   s data structure and of the object   s methods    Just as the fields of a C structure are in a protected namespace  so  are an object   s instance variables  Method names are also protected  Unlike the names of C functions  method names aren   t global symbols  The name of a method    in one class    can   t conflict with method names in other classes     two very different    classes can implement identically named    methods    Method names are part of an object   s interface  When a message is sent requesting that an object do something  the message names the method the object should perform  Because different objects can have methods with the same name  the meaning of a message must be understood relative to the particular object that receives the message  The same message sent to two different objects can invoke two distinct methods   The main benefit of polymorphism is that it simplifies the programming interface  It permits conventions to be established that can be reused in class after class  Instead of inventing a new name for each new function you add to a program  the same names can be reused  The programming interface can be described as a set of abstract behaviors  quite apart from the classes that implement them   Examples   Example-1  Here is a simple example written in Python 2 x   class Animal      def   init   self  name        Constructor of the class         self name   name     def talk self                  Abstract method  defined by convention only         raise NotImplementedError  Subclass must implement abstract method    class Cat Animal       def talk self           return  Meow    class Dog Animal       def talk self           return  Woof  Woof    animals    Cat  Missy               Dog  Lassie     for animal in animals      print animal name          animal talk     Example-2  Polymorphism is implemented in Java using method overloading and method overriding concepts   Let us Consider Car example for discussing the polymorphism  Take any brand like Ford  Honda  Toyota  BMW  Benz etc   Everything is  of type Car   But each have their own advanced features and more advanced technology involved in their move behavior   Now let us create a basic type Car  Car java  public class Car        int price      String name      String color       public void move        System out println  Basic Car move               Let us implement the Ford Car example   Ford extends the type Car to inherit all its members properties and methods    Ford java  public class Ford extends Car    public void move        System out println  Moving with V engine            The above Ford class extends the Car class and also implements the move   method  Even though the move method is already available to Ford through the Inheritance  Ford still has implemented the method in its own way  This is called method overriding   Honda java  public class Honda extends Car    public void move        System out println  Move with i-VTEC engine            Just like Ford  Honda also extends the Car type and implemented the move method in its own way   Method overriding is an important feature to enable the Polymorphism  Using Method overriding  the Sub types can change the way the methods work that are available through the inheritance   PolymorphismExample java  public class PolymorphismExample     public static void main String   args        Car car   new Car        Car f   new Ford        Car h   new Honda         car move        f move        h move             Polymorphism Example Output   In the PolymorphismExample class main method  i have created three objects- Car  Ford and Honda  All the three objects are referred by the Car type    Please note an important point here that A super class type can refer to a Sub class type of object but the vice-verse is not possible  The reason is that all the members of the super class are available to the subclass using inheritance and during the compile time  the compiler tries to evaluate if the reference type we are using has the method he is trying to access    So  for the references car f and h in the PolymorphismExample  the move method exists from Car type  So  the compiler passes the compilation process without any issues   But when it comes to the run time execution  the virtual machine invokes the methods on the objects which are sub types  So  the method move   is invoked from their respective implementations   So  all the objects are of type Car  but during the run time  the execution depends on the Object on which the invocation happens  This is called polymorphism

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I ve provided a high-level overview of polymorphism for another question   Polymorphism in c    Hope it helps   An extract           it helps to start from a simple test for it and definition of  polymorphism   Consider the code    Type1 x  Type2 y   f x   f y        Here  f   is to perform some operation and is being given the values x and y as inputs  To be polymorphic  f   must be able to operate with values of at least two distinct types  e g  int and double   finding and executing type-appropriate code      continued at Polymorphism in c

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Polymorphism       Different execution according to the instance of the class  not the type of reference variable    An interface type reference variable can refer to any of the class instances that implement that interface

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If anybody says CUT to these people   The Surgeon The Hair Stylist The Actor   What will happen    The Surgeon would begin to make an incision  The Hair Stylist would begin to cut someone s hair  The Actor would abruptly stop acting out of the current scene  awaiting directorial guidance    So above representation shows What is polymorphism  same name  different behavior  in OOP   If you are going for an interview and interviewer asks you tell show a live example for polymorphism in the same room we are sitting at  say-  Answer - Door   Windows  Wondering How   Through Door   Window - a person can come  air can come  light can come  rain can come  etc   To understand it better and in a simple manner I used above example   If you need reference for code follow above answers

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Polymorphism in coding terms is when your object can exist as multiple types through inheritance etc  If you create a class named  Shape  which defines the number of sides your object has then you can then create a new class which inherits it such as  Square   When you subsequently make an instance of  Square  you can then cast it back and forward from  Shape  to  Square  as required

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Simple Explanation by analogy  The President of the United States employs polymorphism  How  Well  he has many advisers    Military Advisers Legal Advisers Nuclear physicists  as advisers  Medical advisers  etc etc    Everyone Should only be responsible for one thing  Example    The president is not an expert in zinc coating  or quantum physics  He doesn t know many things - but he does know only one thing  how to run the country    It s kinda the same with code  concerns and responsibilities should be separated to the relevant classes people  Otherwise you d have the president knowing literally everything in the world - the entire Wikipedia  Imagine having the entire wikipedia in a class of your code  it would be a nightmare to maintain   Why is that a bad idea for a president to know all these specific things   If the president were to specifically tell people what to do  that would mean that the president needs to know exactly what to do  If the president needs to know specific things himself  that means that when you need to make a change  then you ll need to make it in two places  not just one   For example  if the EPA changes pollution laws then when that happens  you d have to make a change to the EPA Class and also the President class  Changing code in two places rather than one can be dangerous - because it s much harder to maintain   Is there a better approach   There is a better approach  the president does not need to know the specifics of anything - he can demand the best advice  from people specifically tasked with doing those things       He can use a polymorphic approach to running the country    Example - of using a polymorphic approach   All the president does is ask people to advise him - and that s what he actually does in real life - and that s what a good president should do  his advisors all respond differently  but they all know what the president means by  Advise    He s got hundreds of people streaming into his office  It doesn t actually matter who they are  All the president knows is that when he asks them to  Advise  they know how to respond accordingly   public class MisterPresident       public void RunTheCountry                    assume the Petraeus and Condi classes etc are instantiated          petraeus Advise         Petraeus says send 100 000 troops to Fallujah         condolezza Advise         she says negotiate trade deal with Iran         healthOfficials Advise         they say we need to spend  50 billion on ObamaCare           This approach allows the president to run the country literally without knowing anything about military stuff  or health care or international diplomacy  the details are left to the experts  The only thing the president needs to know is this   Advise      What you DON T want   public class MisterPresident       public void RunTheCountry                    people walk into the Presidents office and he tells them what to do            depending on who they are              Fallujah Advice - Mr Prez tells his military exactly what to do          petraeus IncreaseTroopNumbers            petraeus ImproveSecurity            petraeus PayContractors                Condi diplomacy advice - Prez tells Condi how to negotiate          condi StallNegotiations            condi LowBallFigure            condi FireDemocraticallyElectedIraqiLeaderBecauseIDontLikeHim                Health care          healthOfficial IncreasePremiums            healthOfficial AddPreexistingConditions              NO  NO  NO  In the above scenario  the president is doing all the work  he knows about increasing troop numbers and pre-existing conditions  This means that if middle eastern policies change  then the president would have to change his commands  as well as the Petraeus class as well  We should only have to change the Petraeus class  because the President shouldn t have to get bogged down in that sort of detail  He doesn t need to know about the details  All he needs to know is that if he makes one order  everything will be taken care of  All the details should be left to the experts    This allows the president to do what he does best  set general policy  look good and play golf  P   How is it actually implemented - through a base class or a common interface  That in effect is polymorphism  in a nutshell  How exactly is it done  Through  implementing a common interface  or by using a base class  inheritance  - see the above answers which detail this more clearly   In order to more clearly understand this concept you need to know what an interface is  and you will need to understand what inheritance is  Without that  you might struggle    In other words  Petraeus  Condi and HealthOfficials would all be classes which  implement an interface  - let s call it the IAdvisor interface which just contains one method  Advise    But now we are getting into the specifics    This would be ideal      public class MisterPresident                      You can pass in any advisor  Condi  HealthOfficials                  Petraeus etc  The president has no idea who it will                 be  But he does know that he can ask them to  advise                  and that s all Mr Prez cares for           public void RunTheCountry IAdvisor governmentOfficer                                     governmentOfficer Advise                                        public class USA               MisterPresident president           public USA MisterPresident president                        this president   president                     public void ImplementPolicy                         IAdvisor governmentOfficer   getAdvisor       Returns an advisor  could be condi  or petraus etc              president RunTheCountry governmentOfficer                     Summary  All that you really need to know is this     The president doesn t need to know the specifics - those are left to others  All the president needs to know is to ask who ever walks in the door to advice him - and we know that they will absolutely know what to do when asked to advise  because they are all in actuality  advisors  or IAdvisors        I really hope it helps you  If you don t understand anything post a comment and i ll try again

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What is polymorphism   Polymorphism is the ability to    Invoke an operation on an instance of a specialized type by only knowing its generalized type while calling the method of the specialized type and not that of the generalized type  it is dynamic polymorphism  Define several methods having the save name but having differents parameters  it is static polymorphism    The first if the historical definition and the most important   What is polymorphism used for   It allows to create strongly-typed consistency of the class hierarchy and to do some magical things like managing lists of objects of differents types without knowing their types but only one of their parent type  as well as data bindings   Strong and weak typing  Sample  Here are some Shapes like Point  Line  Rectangle and Circle having the operation Draw   taking either nothing or either a parameter to set a timeout to erase it   public class Shape    public virtual void Draw         DoNothing        public virtual void Draw int timeout        DoNothing          public class Point   Shape    int X  Y   public override void Draw         DrawThePoint          public class Line   Point    int Xend  Yend   public override Draw         DrawTheLine          public class Rectangle   Line    public override Draw         DrawTheRectangle          var shapes   new List lt Shape gt    new Point 0 0   new Line 0 0 10 10   new rectangle 50 50 100 100      foreach   var shape in shapes     shape Draw      Here the Shape class and the Shape Draw   methods should be marked as abstract   They are not for to make understand   Explaination  Without polymorphism  using abstract-virtual-override  while parsing the shapes  it is only the Spahe Draw   method that is called as the CLR don t know what method to call  So it call the method of the type we act on  and here the type is Shape because of the list declaration  So the code do nothing at all   With polymorphism  the CLR is able to infer the real type of the object we act on using what is called a virtual table  So it call the good method  and here calling Shape Draw   if Shape is Point calls the Point Draw    So the code draws the shapes   More readings  C  - Polymorphism  Level 1   Polymorphism in Java  Level 2   Polymorphism  C  Programming Guide   Virtual method table

[oop] What is polymorphism, what is it for, and how is it used?

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