Simple Java Programs

// Prime Number 

import java.util.Scanner;
class Firstday{
    public static void main(String[] args) {
        // Prime Number 
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        int count = 0;
        if (num % num == 0){
            count++;
            if (num % 1 == 0){
                count++;
                if (num % 2 == 0){
                    count++;
                }
                else if (num % 3 == 0){
                    count++;
                }
                else if (num % 5 ==0){
                    count++;
                }
            }
        }

        if (count > 2){
            System.out.println("The Number is not prime");
        }
        else{
            System.out.println("The number is prime");
        }
    }
}


// Maximum of three numbers

import java.util.Scanner;
class Firstday{
    public static void main(String[] args) { 
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a: ");
        int a = sc.nextInt();
        System.out.print("Enter b: ");
        int b = sc.nextInt();
        System.out.print("Enter c: ");
        int c = sc.nextInt();
        int max = Math.max(c, Math.max(a, b));
        System.out.println("The Maximum Number is "+ max);
    }
}

// Factorial of a number (Imp)

import java.util.Scanner;
class Secondday{
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int num = input.nextInt();
        int i = 1;
        int fact = 1;
        while (i <= num){
            fact = fact * i;
            i++;
        }
        System.out.println("The factorial of the number is "+ fact);
    }
}

// Fibonacci series element of a number (Imp)

import java.util.Scanner;
class Secondday{
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int num = input.nextInt();
        int a = 0;
        int b = 1;
        int count = 2;
        while (count <= num){
            int temp = a;
            a = a + b;
            b = temp;
            count++;
        }
        System.out.println(a);
    }  
     
}


// Armstrong Number

import java.lang.Math;
import java.util.Scanner;
public class ThirdDay {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter the number: ");
        int num = input.nextInt();
        int originalnum = num;
        int rem;
        int count = 0;
        while(originalnum != 0){
            rem = originalnum % 10;
            count += Math.pow(rem, 3);
            originalnum = originalnum / 10;
        }

        if (count == num){
            System.out.println("This is an Armstrong Number");
        }
        else{
            System.out.println("This is not an Armstrong Number");
        }

    }
}


//Swapping of two numbers
import java.util.Scanner;
class HelloWorld {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int num1 = input.nextInt();
        int num2 = input.nextInt();
        swap(num1, num2);
        System.out.println("Values of a and b are swapped which are: " + num1 + " " + num2);
        
    }
    static void swap(int a, int b){
        int temp = a;  
        a = b;
        b = temp;
        // This change will only be valid in this function scope only. 
    } 
}
//In the above code, swapping didn't take place because a and b are being new object inside the swap function that's why outside of the swap method, they aren't getting swapped.