Practice Java Programs for Beginner

This repository is dedicated to beginners for learning and practicing basic Java programming concepts through simple, foundational exercises and examples.

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1. Hello World

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Output:
Hello, World!

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2. Add Two Numbers

public class AddNumbers {
    public static void main(String[] args) {
        int num1 = 5;
        int num2 = 7;
        int sum = num1 + num2;
        System.out.println("Sum: " + sum);
    }
}

Output:
Sum: 12

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3. Check Even/Odd

import java.util.Scanner;

public class EvenOdd {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();
        
        if (num % 2 == 0) {
            System.out.println(num + " is even");
        } else {
            System.out.println(num + " is odd");
        }
        scanner.close();
    }
}

Sample Output:
Enter a number: 9
9 is odd

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4. Find Largest of Three Numbers

public class LargestNumber {
    public static void main(String[] args) {
        int a = 25, b = 18, c = 30;
        int largest = (a > b) ? (a > c ? a : c) : (b > c ? b : c);
        System.out.println("Largest: " + largest);
    }
}

Output:
Largest: 30

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5. Simple Calculator

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter first number: ");
        double num1 = scanner.nextDouble();
        System.out.print("Enter operator (+, -, *, /): ");
        char operator = scanner.next().charAt(0);
        System.out.print("Enter second number: ");
        double num2 = scanner.nextDouble();
        
        double result;
        switch(operator) {
            case '+': result = num1 + num2; break;
            case '-': result = num1 - num2; break;
            case '*': result = num1 * num2; break;
            case '/': result = num1 / num2; break;
            default: 
                System.out.println("Invalid operator");
                return;
        }
        System.out.println("Result: " + result);
        scanner.close();
    }
}

Sample Output:
Enter first number: 10
Enter operator: *
Enter second number: 5
Result: 50.0

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6. Print Multiplication Table

import java.util.Scanner;

public class MultiplicationTable {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();
        
        for(int i = 1; i <= 10; i++) {
            System.out.println(num + " x " + i + " = " + (num * i));
        }
        scanner.close();
    }
}

Sample Output (Input: 5):

5 x 1 = 5
5 x 2 = 10
...
5 x 10 = 50

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7. Check Prime Number

import java.util.Scanner;

public class PrimeCheck {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();
        boolean isPrime = true;
        
        if(num <= 1) isPrime = false;
        else {
            for(int i = 2; i <= Math.sqrt(num); i++) {
                if(num % i == 0) {
                    isPrime = false;
                    break;
                }
            }
        }
        
        System.out.println(isPrime ? "Prime" : "Not Prime");
        scanner.close();
    }
}

Sample Output:
Enter a number: 17
Prime

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8. Reverse a Number

import java.util.Scanner;

public class ReverseNumber {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();
        int reversed = 0;
        
        while(num != 0) {
            int digit = num % 10;
            reversed = reversed * 10 + digit;
            num /= 10;
        }
        System.out.println("Reversed: " + reversed);
        scanner.close();
    }
}

Sample Output:
Enter a number: 1234
Reversed: 4321

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9. Find Factorial (Using Recursion)

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = scanner.nextInt();
        System.out.println("Factorial: " + factorial(num));
        scanner.close();
    }
    
    static long factorial(int n) {
        if(n == 0) return 1;
        return n * factorial(n - 1);
    }
}

Sample Output:
Enter a number: 5
Factorial: 120

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10. Fibonacci Series

import java.util.Scanner;

public class Fibonacci {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter terms: ");
        int n = scanner.nextInt();
        
        int a = 0, b = 1;
        System.out.print("Fibonacci Series: ");
        for(int i = 1; i <= n; i++) {
            System.out.print(a + " ");
            int next = a + b;
            a = b;
            b = next;
        }
        scanner.close();
    }
}