Object-oriented programming for Java - 6

Java Polymorphism

1. Java Polymorphism

Java Polymorphism use in the same entity (method or operator or object) can perform different operations in different scenarios.


x
class Polygon {
  public void render() {
    System.out.println("Rendering Polygon...")
  }
}
class Square extends Polygon {
  public void render() {
    System.out.println("Rendering Square...")
  }
}
class Circle extends Polygon {
  public void render() {
    System.out.println("Rendering Circle...")
  }
}
class Main {
  public static void main(String[] args) {
    Square square = new Square();
    square.render();
    
    Circle circle = new Circle();
    circle.render();
  }
}
// output:
// Rendering Square...
// Rendering Circle...

In this example, the render() method perform different in each Class. In here we can point the render() method is Polymorphism.

2. Polymorphism using method overriding


x
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) {
    Language lang = new Language();
    lang.displayInfo();
    
    Java java = new Java();
    java.displayInfo();
  }
}
// output:
// Common English Language
// Java Programming Language

Workflow:

Working of Java Polymorphism

3. Polymorphism using method overloading


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class Pattern {
  public void display() {
    for (int i = 0; i < 10; i++) {
      System.out.println("*");
    }
  }
  
  public void display(char symbol) {
    for (int i = 0; i < 10; i++) {
      System.out.println(symbol);
    }
  }
}
class Main {
  public static void main(String[] args) {
    Pattern pattern = new Pattern();
    pattern.display();
    System.out.println();
    pattern.display("#");
  }
}
// output:
// **********
// 
// ##########

Compare


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// method with no arguments
display() {
  ...
}
// method with a single char type argument
display(char symbol) {
  ...
}

3. Java Operator Overloading

(a). For int


xxxxxxxxxx
int a = 5;
int b = 6;
// + with numbers
int sum = a + b;  // Output = 11

(b). For String


String first = "Java ";
String second = "Programming";
// + with strings
name = first + second;  // Output = Java Programming

4. Polymorphic Variables

Polymorphic Variable: if it refers to different values under different conditions.

Object variables (instance variables) represent the behavior of polymorphic variables in Java.


x
class ProgrammingLanguage {
  public void display() {
    System.out.println("I am Programming Language.");
  }
}
class Java extends ProgrammingLanguage {
  @Override
  public void display() {
    System.out.println("I am Object-Oriented Programming Language.");
  }
}
class Main {
  public static void main(String[] args) {
    ProgrammingLanguage pl;
    
    pl = new ProgrammingLanguage();
    pl.display();
    pl = new Java();
    pl.display();
  }
}
// output:
// I am Programming Language.
// I am Object-Oriented Programming Language.