Practical on Java constructor and methods

 Example 1: Constructor and Instance Method

public class Person {

    // Instance variables

    String name;

    int age;


    // Constructor

    public Person(String n, int a) {

        name = n;

        age = a;

    }


    // Instance method

    public void displayInfo() {

        System.out.println("Name: " + name);

        System.out.println("Age: " + age);

    }


    public static void main(String[] args) {

        // Creating an object using the constructor

        Person person1 = new Person("John", 25);


        // Calling the method to display information

        person1.displayInfo();

    }

}

Output:

Name: John

Age: 25


Example 2: Parameterized Method

public class Calculator {

    // Method to add two numbers

    public int add(int num1, int num2) {

        return num1 + num2;

    }


    public static void main(String[] args) {

        // Creating an object of the class

        Calculator calc = new Calculator();


        // Calling the method and displaying the result

        System.out.println("Sum: " + calc.add(10, 20));

    }

}

Output:

Sum: 30


Example 3: Overloaded Constructors

public class Book {

    // Instance variables

    String title;

    String author;


    // Constructors

    public Book(String t, String a) {

        title = t;

        author = a;

    }


    public Book(String t) {

        title = t;

        author = "Unknown";

    }


    // Instance method

    public void displayInfo() {

        System.out.println("Title: " + title);

        System.out.println("Author: " + author);

    }


    public static void main(String[] args) {

        // Creating objects using different constructors

        Book book1 = new Book("Java Programming", "John Doe");

        Book book2 = new Book("Python Basics");


        // Calling the method to display information

        book1.displayInfo();

        System.out.println();

        book2.displayInfo();

    }

}

Output:

Title: Java Programming

Author: John Doe

Title: Python Basics

Author: Unknown


Example 4: Static Method

public class MathOperations {

    // Static method to calculate square

    public static int square(int num) {

        return num * num;

    }


    public static void main(String[] args) {

        // Calling the static method directly

        int result = MathOperations.square(5);


        // Displaying the result

        System.out.println("Square: " + result);

    }

}

Output:

Square: 25


Example 5: Method with Return Value

import java.util.Scanner;

public class CircleArea {

    // Method to calculate area of a circle

    public double calculateArea(double radius) {

        return Math.PI * radius * radius;

    }


    public static void main(String[] args) {

        // Creating an object of the class

        CircleArea circle = new CircleArea();


        // Taking user input for radius

        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter the radius of the circle: ");

        double userRadius = scanner.nextDouble();


        // Calling the method and displaying the result

        double area = circle.calculateArea(userRadius);

        System.out.println("Area of the circle: " + area);

    }

}

Output:

Enter the radius of the circle: 3.5

Area of the circle: 38.48451000647496


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