In this article, you will learn-
Java Polymorphism
In this tutorial, we will find out about Java polymorphism and its implementation with the help of examples.
Polymorphism is a significant concept of object-oriented programming. It essentially implies more than one structure.
That is, a similar entity (method or operator or objects) can perform various tasks in various scenarios.
Example: Java Polymorphism
class Polygon {
// method to render a shape
public void render() {
System.out.println("Rendering Polygon...");
}
}
class Square extends Polygon {
// renders Square
public void render() {
System.out.println("Rendering Square...");
}
}
class Circle extends Polygon {
// renders circle
public void render() {
System.out.println("Rendering Circle...");
}
}
class Main {
public static void main(String[] args) {
// create an object of Square
Square s1 = new Square();
s1.render();
// create an object of Circle
Circle c1 = new Circle();
c1.render();
}
}
Output
Rendering Square...
Rendering Circle...
In the above example, we have created a superclass: Polygon and two subclasses: Square and Circle. Notice the use of the render() method.
The main purpose of the render() method is to render the shape. However, the process of rendering a square is different than the process of rendering a circle.
Hence, the render() method behaves differently in different classes. Or, we can say render() is polymorphic.
Why Polymorphism?
Polymorphism allows us to make reliable code. In the past example, we can likewise make various methods: renderSquare() and renderCircle() to deliver Square and Circle, respectively.
This will work perfectly. In any case, for each shape, we have to make various methods. It will make our code conflicting.
To solve this, polymorphism in Java allows us to make a single method render() that will act diversely for various shapes.
Note: The print() method is additionally a case of polymorphism. It is used to print values of various sorts like char, int, string, etc.
We can achieve polymorphism in Java using the following ways:
- Method Overriding
- Method Overloading
- Operator Overloading
Java Method Overriding
During inheritance in Java, if a similar method is available in both the superclass and the subclass. At that point, the method in the subclass overrides a similar method in the superclass. This is called method overriding.
For this situation, a similar strategy will perform one activity in the superclass and another activity in the subclass. For instance,
Example 1: Polymorphism using method overriding
class Language {
public void displayInfo() {
System.out.println("Common English Language");
}
}
class Java extends Language {
@Override
public void displayInfo() {
System.out.println("Java Programming Language");
}
}
class Main {
public static void main(String[] args) {
// create an object of Java class
Java j1 = new Java();
j1.displayInfo();
// create an object of Language class
Language l1 = new Language();
l1.displayInfo();
}
}
Output
Java Programming Language
Common English Language
In the above example, we have created a superclass named Language and a subclass named Java. Here, the method displayInfo() is present in both Language and Java.
The use of displayInfo() is to print the information. However, it is printing different information in Language and Java.
Based on the object used to call the method, the corresponding information is printed.
Note: The method that is called is resolved during the execution of the program. Subsequently, method overriding is a run-time polymorphism.
2. Java Method Overloading
In a Java class, we can make methods with a similar name if they differ in parameters. For instance,
void func() { ... }
void func(int a) { ... }
float func(double a) { ... }
float func(int a, float b) { ... }
This is known as method overloading in Java. Here, a similar method will perform various activities based on the parameter.
Example 3: Polymorphism using method overloading
class Pattern {
// method without parameter
public void display() {
for (int i = 0; i < 10; i++) {
System.out.print("*");
}
}
// method with single parameter
public void display(char symbol) {
for (int i = 0; i < 10; i++) {
System.out.print(symbol);
}
}
}
class Main {
public static void main(String[] args) {
Pattern d1 = new Pattern();
// call method without any argument
d1.display();
System.out.println("\n");
// call method with a single argument
d1.display('#');
}
}
Output
**********
##########
In the above example, we have created a class named Pattern. The class contains a method named display() that is overloaded.
// method with no arguments
display() {...}
// method with a single char type argument
display(char symbol) {...}
Here, the main function of display() is to print the pattern. However, based on the arguments passed, the method is performing different operations:
prints a pattern of *, if no argument is passed or
prints pattern of the parameter, if a single char type argument is passed.
Note: The method that is called is dictated by the compiler. Subsequently, it is otherwise called arrange time polymorphism.
3. Java Operator Overloading
Some operators in Java behave differently with different operands. For example,
- + operator is overloaded to perform numeric addition as well as string concatenation, and
- operators like &, |, and ! are overloaded for logical and bitwise operations.
Let’s see how we can achieve polymorphism using operator overloading.
- The + operator is used to include two substances. However, in Java, the + operator performs two tasks.
- When + is used with numbers (integers and floating-point numbers), it performs mathematical addition. For instance,
int a = 5;
int b = 6;
// + with numbers
int sum = a + b; // Output = 11
When we use the + operator with strings, it will perform string concatenation (join two strings). For example,
String first = "Java ";
String second = "Programming";
// + with strings
name = first + second; // Output = Java Programming
Here, we can see that the + operator is overloaded in Java to perform two tasks: addition and concatenation.
Note: In languages like C++, we can characterize operators to work diversely for various operands. Be that as it may, Java doesn’t support user-defined operator overloading.
Polymorphic Variables
A variable is called polymorphic if it refers to various qualities under various conditions.
Object variables (instance variables) represent to the behaviour of polymorphic variables in Java. It is on the grounds that object variables of a class can refer to objects of its class as well as objects of its subclasses.
Example: Polymorphic Variables
class ProgrammingLanguage {
public void display() {
System.out.println("This is Programming Language.");
}
}
class Java extends ProgrammingLanguage {
@Override
public void display() {
System.out.println("This is Java.");
}
}
class Main {
public static void main(String[] args) {
// declare an object variable
ProgrammingLanguage pl;
// create object of Animal class
pl = new ProgrammingLanguage();
pl.display();
// create object of Java class
pl = new Java();
pl.display();
}
}
Output
This is Programming Language.
This is Java.
In the above example, we have created an object variable pl of the ProgrammingLanguage class. Here, pl is a polymorphic variable. This is because,
In statement pl = new ProgrammingLanguage(), pl refer to the object of the ProgrammingLanguage class.
And, in statement pl = new Java(), pl refer to the object of the Java class.
This is an example of upcasting in Java. To learn more, visit Java upcasting and downcasting.
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