What is the main difference between Inheritance and Polymorphism

Question

I was presented with this question in an end of module open book exam today and found myself lost  I was reading Head first Javaand both definitions seemed to be exactly the same  I was just wondering what the MAIN difference was for my own piece of mind  I know there are a number of similar questions to this but  none I have seen which provide a definitive answer

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Polymorphism is an effect of inheritance  It can only happen in classes that extend one another  It allows you to call methods of a class without knowing the exact type of the class  Also  polymorphism does happen at run time   For example  Java polymorphism example     Inheritance lets derived classes share interfaces and code of their base classes  It happens at compile time   For example  All Classes in the Java Platform are Descendants of Object  image courtesy Oracle      To learn more about Java inheritance and Java polymorphism

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inheritance is kind of polymorphism  Exactly in fact inheritance is the dynamic polymorphism  So  when you remove inheritance you can not override anymore

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If you use JAVA it s as simple as this   Polymorphism is using inherited methods but  Overriding  them to do something different  or the same if you call super so wouldn t technically be polymorphic    Correct me if I m wrong

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Inheritance is a concept related to code reuse  For example if I have a parent class say Animal and it contains certain attributes and methods  for this example say makeNoise   and sleep    and I create two child classes called Dog and Cat  Since both dogs and cats go to sleep in the same fashion  I would assume  there is no need to add more functionality to the sleep   method in the Dog and Cat subclasses provided by the parent class Animal  However  a Dog barks and a Cat meows so although the Animal class might have a method for making a noise  a dog and a cat make different noises relative to each other and other animals  Thus  there is a need to redefine that behavior for their specific types  Thus the definition of polymorphism  Hope this helps

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The main difference is polymorphism is a specific result of inheritance   Polymorphism is where the method to be invoked is determined at runtime based on the type of the object   This is a situation that results when you have one class inheriting from another and overriding a particular method  However  in a normal inheritance tree  you don t have to override any methods and therefore not all method calls have to be polymorphic   Does that make sense  It s a similar problem to all Ford vehicles are automobiles  but not all automobiles are Fords  although not quite        Additionally  polymorphism deals with method invocation whereas inheritance also describes data members  etc

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Inheritance is when class A inherits all nonstatic protected public methods fields from all its parents till Object

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In Java  the two are closely related  This is because Java uses a technique for method invocation called  dynamic dispatch   If I have  public class A     public void draw             public void spin              public class B extends A     public void draw             public void bad                   A testObject   new B     testObject draw       calls B s draw  polymorphic testObject spin       calls A s spin  inherited by B testObject bad       compiler error  you are manipulating this as an A   Then we see that B inherits spin from A  However  when we try to manipulate the object as if it were a type A  we still get B s behavior for draw  The draw behavior is polymorphic   In some languages  polymorphism and inheritance aren t quite as closely related  In C    for example  functions not declared virtual are inherited  but won t be dispatched dynamically  so you won t get that polymorphic behavior even when you use inheritance    In javascript  every function call is dynamically dispatched and you have weak typing  This means you could have a bunch of unrelated objects  each with their own draw  have a function iterate over them and call the function  and each would behave just fine  You d have your own polymorphic draw without needing inheritance

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Inheritance is when a  class  derives from an existing  class    So if you have a Person class  then you have a Student class that extends Person  Student inherits all the things that Person has   There are some details around the access modifiers you put on the fields methods in Person  but that s the basic idea   For example  if you have a private field on Person  Student won t see it because its private  and private fields are not visible to subclasses   Polymorphism deals with how the program decides which methods it should use  depending on what type of thing it has   If you have a Person  which has a read method  and you have a Student which extends Person  which has its own implementation of read  which method gets called is determined for you by the runtime  depending if you have a Person or a Student   It gets a bit tricky  but if you do something like  Person p   new Student    p read      the read method on Student gets called   Thats the polymorphism in action   You can do that assignment because a Student is a Person  but the runtime is smart enough to know that the actual type of p is Student   Note that details differ among languages   You can do inheritance in javascript for example  but its completely different than the way it works in Java

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The main purpose of polymorphism   To create reference variable to super class and holding the subclass object     an object can perform multiple behaviours    In inheritance  subclass inherit the properties of super class

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Inheritance is more a static thing  one class extends another  while polymorphism is a dynamic  runtime thing  an object behaves according to its dynamic  runtime type not to its static  declaration type    E g      This assignment is possible because B extends A A a   new B       polymorphic call  access a foo      -  Though the static  declaration type of a is A  the actual dynamic  runtime type is B and thus a foo   will execute foo as defined in B not in A

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Polymorphism is achieved by Inheritance in Java    -- Animal  --  instances       -- Cat      -- Hamster      -- Lion      -- Moose   -- interface-for-diet       -- Carnivore       -- Herbivore  -- interface-for-habitat       -- Pet       -- Wild  public class Animal       void breath               public interface Carnivore       void loveMeat       public interface Herbivore       void loveGreens       public interface Pet       void liveInside       public interface Wild       void liveOutside       public class Hamster extends Animal implements Herbivore  Pet         Override     public void liveInside             System out println  I live in a cage and my neighbor is a Gerbil                Override     public void loveGreens             System out println  I eat Carrots  Grapes  Tomatoes  and More             public class Cat extends Animal implements Carnivore  Pet        Override     public void liveInside             System out println  I live in a cage and my neighbr is a Gerbil                Override     public void loveMeat             System out println  I eat Tuna  Chicken  and More             public class Moose extends Animal implements Herbivore  Wild         Override     public void liveOutside             System out println  I live in the forest                Override     public void loveGreens             System out println  I eat grass             public class Lion extends Animal implements Carnivore  Wild         Override     public void liveOutside             System out println  I live in the forest                Override     public void loveMeat             System out println  I eat Moose              Hamster class inherits structure from Animal  Herbivore and Pet to exhibit Polymorphic behaviorism of a domestic pet   Cat class inherits structure from Animal  Carnivore and Pet to also exhibit Polymorphic behaviorism of a domestic pet

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Polymorphism  Suppose you work for a company that sells pens  So you make a very nice class called  Pen  that handles everything that you need to know about a pen  You write all sorts of classes for billing  shipping  creating invoices  all using the Pen class  A day boss comes and says   Great news  The company is growing and we are selling Books  amp  CD s now   Not great news because now you have to change every class that uses Pen to also use Book  amp  CD  But what if you had originally created an interface called  SellableProduct   and Pen implemented this interface  Then you could have written all your shipping  invoicing  etc classes to use that interface instead of Pen  Now all you would have to do is create a new class called Book  amp  CompactDisc which implements the SellableProduct interface  Because of polymorphism  all of the other classes could continue to work without change  Make Sense   So  it means using Inheritance which is one of the way to achieve polymorphism   Polymorhism can be possible in a class   interface but Inheritance always between 2 OR more classes   interfaces  Inheritance always conform  is-a  relationship whereas it is not always with Polymorphism  which can conform both  is-a     has-a  relationship

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Polymorphism  The ability to treat objects of different types in a similar manner   Example  Giraffe and Crocodile are both Animals  and animals can Move   If you have an instance of an Animal then you can call Move without knowing or caring what type of animal it is   Inheritance  This is one way of achieving both Polymorphism and code reuse at the same time   Other forms of polymorphism  There are other way of achieving polymorphism  such as interfaces  which provide only polymorphism but no code reuse  sometimes the code is quite different  such as Move for a Snake would be quite different from Move for a Dog  in which case an Interface would be the better polymorphic choice in this case   In other dynamic languages polymorphism can be achieved with Duck Typing  which is the classes don t even need to share the same base class or interface  they just need a method with the same name   Or even more dynamic like Javascript  you don t even need classes at all  just an object with the same method name can be used polymorphically

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Oracle documentation quoted the difference precisely    inheritance   A class inherits fields and methods from all its superclasses  whether direct or indirect  A subclass can override methods that it inherits  or it can hide fields or methods that it inherits   Note that hiding fields is generally bad programming practice    polymorphism   polymorphism refers to a principle in biology in which an organism or species can have many different forms or stages  This principle can also be applied to object-oriented programming and languages like the Java language  Subclasses of a class can define their own unique behaviors and yet share some of the same functionality of the parent class   polymorphism is not applicable for fields    Related post   Polymorphism vs Overriding vs Overloading

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Inheritance refers to using the structure and behavior of a super class in a subclass    Polymorphism refers to changing the behavior of a super class in the subclass

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Polymorphism is an approach to expressing common behavior between types of objects that have similar traits  It also allows for variations of those traits to be created through overriding  Inheritance is a way to achieve polymorphism through an object hierarchy where objects express relationships and abstract behaviors  It isn t the only way to achieve polymorphism though  Prototype is another way to express polymorphism that is different from inheritance  JavaScript is an example of a language that uses prototype  I d imagine there are other ways too

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With Inheritance the implementation is defined in the superclass -- so the behavior is inherited   class Animal     double location    void move double newLocation          location   newLocation         class Dog extends Animal    With Polymorphism the implementation is defined in the subclass -- so only the interface is inherited   interface Animal     void move double newLocation      class Dog implements Animal     double location    void move double newLocation          location   newLocation

[java] What is the main difference between Inheritance and Polymorphism?

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