Difference between Compile Time Polymorphism and Runtime Polymorphism

Thе diffеrеncе bеtwееn Compile-time Polymorphism and Runtimе Polymorphism is that compilе-timе polymorphism, also known as mеthod ovеrloading, occurs whеn multiplе mеthods in a class havе thе samе namе but diffеrеnt paramеtеr lists whereas runtimе polymorphism, also known as mеthod ovеrriding, occurs whеn a subclass providеs a spеcific implеmеntation for a mеthod that is already dеfinеd in its supеrclass. 

• Polymorphism is one of the most fundamental concepts used in Java. 
• Polymorphism implies the fact that a single action/ task can be done through many different methods. 
• In Java, a single message can be displayed in more than one form by using Polymorphism. 
• Polymorphism is of two types- Compile time Polymorphism (also known as Static Polymorphism) and Runtime Polymorphism (also known as Dynamic Polymorphism).

Key Terms- Java, Polymorphism, Compile Time Polymorphism, Runtime Polymorphism

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What is Polymorphism in Java?

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The term Polymorphism means "many forms". In Java, this concept comes into play when there are many classes related to each other by Inheritance. As Inheritance allows us to use attributes and methods from other classes, Polymorphism uses those methods to perform different tasks.

For example, a superclass Animal

And it has a method called animalSound()

Subclasses of Animals could be Cats, Dogs, Lions, Birds - And they also have their own implementation of an animal sound (the dog barks, and the cat meows, etc.):

Now we can create Dog and cat objects and call the animalSound() method on both of them:

In this way Polymorphism helps to reuse attributes and methods of an existing class while creating a new class. 

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Compile Time Polymorphism vs Runtime Polymorphism

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Polymorphism in Java is categorised into Command line Diversity and Runtime Polymorphism. This Command line diversity is Compile Time Polymorphism that works on method overloading. 

• The call for given overloaded methods occurs at the time of compiling the attribute, thus this type of Polymorphism is also known as Static Polymorphism. 
• Here, the parameters influence the type of overloaded method invoked.
• On the other hand, the call Resolution in Runtime Polymorphism occurs at the time of formation of objects rather than at the build time. 
• Runtime Polymorphism applies the use of the method Overriding. 
• The object directly decides the override method to be used at the time of compilation.

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Compile Time Polymorphism

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By definition Compile Time Polymorphism is the coupling of an object with its functionality at its Compile Time. This means that for an object, Java calls the most appropriate method at compile time by evaluating the method signatures.

The following points can help understand compile-time polymorphism more clearly:-

• It is achieved by Method overloading. 
• Method overloading implies that one can have many different methods for the same name and same class but with a distinct prototype. In this way, a single command can be displayed in many ways.
• When function overloading is done at Compile time, Compile Time Polymorphism is made.
• It depends and varies with the type of technology used.
• It is also known as Static Polymorphism or Early Binding. 

Compile Time Polymorphism Example

The example is illustrated below:

Compile Time Polymorphism Example

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Runtime Polymorphism 

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Whenever an object exhibiting polymorphism becomes associated with its functionality at the run time (at the time of display), it is known as Runtime Polymorphism.

• The method to be invoked is evaluated and decided by the Java virtual machine at the Runtime.
• Method Overriding produces Runtime Polymorphism. 
• Method Overriding states that the child class has the same method as its Parent class. This ultimately holds true for the implementation of the method by any of the Parent Classes of the concerned Child class.
• Runtime Polymorphism is also known as Dynamic Polymorphism or Late binding.
• The functional attribute involved can be modified as long as the Runtime has not started. 

Runtime Polymorphism Example

Here is the example of runtime polymorphism:

Runtime Polymorphism Example

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Difference between Compile-Time and Runtime Polymorphism

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In the following table, the main differences between Compile time and Runtime Polymorphism are given:-

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Things to Remember 

• In Java, Polymorphism is a way in which an object can be displayed in different forms.
• Polymorphism is of two types- Compile Polymorphism and Runtime Polymorphism. 
• Compile time Polymorphism occurs when different methods for the same name and same class but differing signatures are used in Java. 
• Runtime Polymorphism is used when the same methods are used for different names and classes related to each other by Inheritance.
• Method overloading produces Compile Time Polymorphism. 
• Method Overriding is used to instil Runtime Polymorphism. 

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