Essential Java Programming Examples and Concepts

Posted on Apr 23, 2026 in Computer Engineering in Information Technologies Engineering

Java Programming Examples

1. Reverse Number and Sum of Digits

import java.util.Scanner;

class SumReverse {
    int n, rev = 0, sum = 0, r;
    Scanner sc = new Scanner(System.in);

    void input() {
        System.out.print("Enter a Number: ");
        n = sc.nextInt();
    }

    void reverse() {
        while (n > 0) {
            r = n % 10;
            rev = rev * 10 + r;
            sum = sum + r;
            n = n / 10;
        }
        System.out.println("Sum of digits: " + sum);
        System.out.println("\nThe Reverse of a Number is: " + rev);
    }

    public static void main(String args[]) {
        SumReverse rr = new SumReverse();
        rr.input();
        rr.reverse();
    }
}

2. Sorting Algorithm (Ascending Order)

import java.util.Scanner;

class Ascending {
    public void arrange() {
        int n, temp;
        Scanner s = new Scanner(System.in);
        System.out.print("Enter no. of elements you want in array: ");
        n = s.nextInt();
        int a[] = new int[n];
        System.out.println("Enter all the elements:");
        for (int i = 0; i < n; i++) {
            a[i] = s.nextInt();
        }
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                if (a[i] > a[j]) {
                    temp = a[i];
                    a[i] = a[j];
                    a[j] = temp;
                }
            }
        }
        System.out.print("Ascending Order: ");
        for (int i = 0; i < n - 1; i++) {
            System.out.print(a[i] + ",");
        }
        System.out.print(a[n - 1]);
    }
}

public class AscendingOrder {
    public static void main(String[] args) {
        Ascending a1 = new Ascending();
        a1.arrange();
    }
}

3. Complex Number Addition

import java.util.Scanner;

public class Complex {
    double real, imag;

    public Complex(double real, double imag) {
        this.real = real;
        this.imag = imag;
    }

    public static void main(String[] args) {
        double r, i;
        Scanner s = new Scanner(System.in);
        System.out.println("Enter the first complex number");
        r = s.nextDouble();
        i = s.nextDouble();
        Complex n1 = new Complex(r, i);
        System.out.println("Enter the second complex number");
        r = s.nextDouble();
        i = s.nextDouble();
        Complex n2 = new Complex(r, i);
        Complex temp = add(n1, n2);
        System.out.printf("Sum = %.1f + %.1fi", temp.real, temp.imag);
    }

    public static Complex add(Complex n1, Complex n2) {
        return new Complex(n1.real + n2.real, n1.imag + n2.imag);
    }
}

4. Static Members

class Numob {
    static int count = 0;
    Numob() {
        count++;
    }
    public static void main(String[] args) {
        new Numob();
        new Numob();
        new Numob();
        new Numob();
        System.out.println("Number of objects created: " + count);
    }
}

5. Method Overloading

import java.util.Scanner;

class Overload {
    double area(float l, float w, float h) { return l * w * h; }
    double area(float l) { return l * l * l; }
    double area(float r, float h) { return 3.1416 * r * r * h; }
}

public class MethodOverloading {
    public static void main(String[] args) {
        Overload o1 = new Overload();
        Scanner s = new Scanner(System.in);
        // Implementation logic follows...
    }
}

6. Inheritance and Student Results

class Student {
    public String name;
    public int a[] = new int[5];
    public int total = 0, avg;
    // Methods for reading and displaying data
}

class Result extends Student {
    public void percentCal() {
        // Calculation logic
    }
}

7. Multilevel Inheritance

class X { X(int i) { System.out.println("Created X"); } }
class Y extends X { Y(int i, int j) { super(i); System.out.println("Created Y"); } }
class Z extends Y { Z(int i, int j, int k) { super(i, j); System.out.println("Created Z"); } }

8. Multithreading

class Odd implements Runnable { public void run() { /* Logic */ } }
class Even implements Runnable { public void run() { /* Logic */ } }

9. Keyboard Events

import java.awt.*;
import java.awt.event.*;

public class KeyExample extends Frame implements KeyListener {
    // AWT implementation for handling keyboard input
}