Java polymorphism

Ability of an organism lớn take different shapes is polymorphism in bio world. A simplest definition in computer terms would be, handling different data types using the same interface. In this tutorial, we will learn about what is polymorphism in computer science và how polymorphism can be used in Java.

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I wish this tutorial will help address the following,

is overloading polymorphism? is overriding polymorphism? Ad hoc Polymorphism Parametric Polymorphism Coercion Polymorphism Inclusion or subtype Polymorphism what is static-binding? what is dynamic binding?

Types of Polymorphism

Polymorphism in computer science was introduced in 1967 by Christopher Strachey. Please let me know with reference if it is not a fact and the tutorial can be updated. Following are the two major types of polymorphism as defined by Strachey.

Ad hoc Polymorphism Parametric Polymorphism

Later these were further categorized as below:


Ad hoc Polymorphism

"Ad-hoc polymorphism is obtained when a function works, or appears to work, on several different types (which may not exhibit a common structure) và may behave sầu in unrelated ways for each type.  Parametric polymorphism is obtained when a function works uniformly on a range of types; these types normally exhibit some comtháng structure." – Strachey 1967

If we want to say the above sầu paragraph in two words, they are operator overloading & function overloading. Determining the operation of a function based on the arguments passed.

Ad hoc Polymorphism in Java

In Java we have sầu function overloading and we vị not have operator overloading. Yes we have “+” operator implemented in a polymorphic way.

String fruits = "Apple" + "Orange";int a = b + c;The definition is when the type is different, the internal function adjusts itself accordingly. int và float are different types & so even the following can be included in polymorphism operator overloading.

int i = 10 - 3;float f = 10.5 - 3.5;Similarly even * & / can be considered as overloaded for int and float types.

Having said all the above sầu, these are all language implemented features. Developers cannot custom overload an operator. So answer for the question, “does Java supports operator overloading?” is “yes & no”.

Java wholeheartedly supports function overloading. We can have sầu same function name with different argument type danh mục. For function overloading in Java I have sầu already written a super-hit tutorial & I am sure you will enjoy reading it.

In inheritance, the ability lớn replace an inherited method in the subclass by providing a different implementation is overriding. Function overriding in is discussed in the same tutorial as overloading.

Polymorphism is a larger concept which consists of all these different types. So it is not right lớn say that overloading or overriding alone is polymorphism. It is more than that.

Coercion Polymorphism

Implicit type conversion is called coercion polymorphism. Assume that we have a function with argument int. If we Hotline that function by passing a float value and if the the run-time is able to convert the type and use it accordingly then it is coercion polymorphism.

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Now with this definition, let us see if Java has coercion polymorphism. The answer is half yes. Java supports widening type conversion and not narrowing conversions.

Narrowing Conversion

class FToC public static float fToC (int fahrenheit) return (fahrenheit - 32)*5/9; public static void main(String args<>) System.out.println(fToC(98.4)); Java does not support narrowing conversion & we will get error as " fToC(int) in FToC cannot be applied lớn (double)"

Widening Conversion

class FToC public static float fToC (float fahrenheit) return (fahrenheit - 32)*5/9; public static void main(String args<>) System.out.println(fToC(98)); The above code will work without an error in Java. We are passing an int value ’98’ wherein the expected value type is a float. Java implicitly converts int value khổng lồ float & it supports widening conversion.

Universal Polymorphism

Universal polymorphism is the ability khổng lồ handle types universally. There will be a common template structure available for operations definition irrespective sầu of the types. Universal polymorphism is categorized into lớn inclusion polymorphism & parametric polymorphism.

Inclusion polymorphism (subtype polymorphism)

Substitutability was introduced by eminent Barbara Liskov & Jeannette Wing. It is also called as Liskov substitution principle.

“Let T be a super type & S be its subtype (parent and child class). Then, instances (objects) of T can be substituted with instances of S.”

Replacing the supertype’s instance with a subtype’s instance. This is called inclusion polymorphism or subtype polymorphism. This is covariant type and the reverse of it is contravariant. We have sầu discussed the substitution principle và covariant types, contravariant & invariant earlier in the linked tutorial. This is demonstrated with a code example. Java supports subtype polymorphism from Java / JDK version 1.5.

Parametric Polymorphism

Here we go, we have sầu come khổng lồ ‘Generics’. This is a nice topic và requires a full detailed tutorial with respect to Java. For now, parametric polymorphism is the ability to lớn define functions and types in a generic way so that it works based on the parameter passed at runtime. All this is done without compromising type-safety.

The following source code demonstrates a generics feature of Java. It gives the ability khổng lồ define a class và parameterize the type involved. The behavior of  the class is based on the parameter type passed when it is instantiated.

package;import java.util.ArrayList;import java.util.List;public class PapersJar private List itemList = new ArrayList();public void add(T item) itemList.add(item);public T get(int index) return itemList.get(index);public static void main(String args<>) PapersJar papersStr = new PapersJar();papersStr.add("Lion");String str = papersStr.get(0);System.out.println(str);PapersJar papersInt = new PapersJar();papersInt.add(new Integer(100));Integer integerObj = papersInt.get(0);System.out.println(integerObj);

Static Binding vs Dynamic Binding

Give sầu all the above polymorphism types, we can classify these under different two broad groups static binding và dynamic binding. It is based on when the binding is done with the corresponding values. If the references are resolved at compile time, then it is static binding and if the references are resolved at runtime then it is dynamic binding. Static binding and dynamic binding also called as early binding và late binding. Sometimes they are also referred as static polymorphism & dynamic polymorphism.

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Let us take overloading and overriding for example khổng lồ understand static & dynamic binding. In the below code, first Gọi is dynamic binding. Whether to lớn Hotline the obey method of DomesticAnimal or Animal is resolve at runtime & so it is dynamic binding. In the second call, whether the method obey() or obey(String i) should be called is decided at compile time & so this is static binding.

package;public class Binding public static void main(String args<>) Animal animal = new DomesticAnimal();System.out.println(animal.obey());DomesticAnimal domesticAnimal = new DomesticAnimal();System.out.println(domesticAnimal.obey("Ok!"));class Animal public String obey() return "No!";class DomesticAnimal extends Animal public String obey() return "Yes!";public String obey(String i) return i;Output:

Yes! Ok!

Advantages of Polymorphism

Generics: Enables generic programming. Extensibility: Extending an already existing system is made simple. De-clutters the object interface and simplifies the class blueprint.

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