Java Program To Find The Factorial Of A Number Using Recursion

In this Java Program, we calculate the factorial of the number using recursion.

Factorial of n is the product of all the positive descending integers. It is denoted by n!

For example : 4! = 4 * 3 * 2 * 1 = 24

Logic : fact = fact * i;

Step 1 : Create main method

Step 2  : Create variable factorial and store factorial of 4 in it.

Step 3  : Print the number

Step 4 : Create a static function which returns 1

Step 5 : Create recursion function which calls itself

Program :

public class FactorialDemo2 {

    public static void main(String[] args){

        int factorial = fact(4);

        System.out.println("Factorial of 4 is:"+factorial);

    }

    static int fact(int n)

    {

    int output;

    if(n==1){

        return 1;

    }

    //Recursion : Function calling itself

    output = fact(n-1)*n;

    return output;

    }

}

Output :

Factorial of 4 is : 24

For execution of the same do visit my YouTube Channel :

https://youtu.be/xGJ2VBxZuRc

Java Program To Find The Factorial Of A Number Using Recursion Entered By The User

In this Java Program, we calculate the factorial of the number using recursion entered by the user.

Factorial of n is the product of all the positive descending integers. It is denoted by n!

For example : 4! = 4 * 3 * 2 * 1 = 24

Logic : fact = fact * i;

Step 1 : Import Scanner Class

Step 2 : Create main method

Step 3 : Create scanner object for capturing the user input

Step 4 : Ask the user to enter the number

Step 5 : Store the entered value in the variable num

Step 6 : Call the user defined function fact

Step 7 : Print the number

Step 8 : Create a static function which returns 1

Step 9 : Create recursion function which calls itself

Program :

import java.util.Scanner;

public class FactorialDemo {

    public static void main(String[] args)

    {

        //Scanner object for capturing the user input

        Scanner sc = new Scanner(System.in);

        System.out.println("Enter the number:");

        //Store the entered value in variable

        int num =sc.nextInt();

        //Call the user defined function fact

        int factorial = fact(num);

        System.out.println("Factorial of entered number is:"+factorial);

    }

    static int fact(int n)

    {

        int output;

        if(n==1){

            return 1;

        }

                //Recursion: Function calling itself

        output = fact(n-1)*n;

        return output;

    }    

}

Output :

Enter the number:

5

Factorial of entered number is:120

For execution of the same do visit my YouTube Channel :

https://youtu.be/IBSxhMDbMrw

Java Program To Reverse a String Entered by the User

In this Java Program, we reverse a string entered by the user

Logic :  String reversed = reverseString(str);

Step 1 : Import Scanner Class

Step 2 : Create main method

Step 3 : Create variable str

Step 4 : Ask user to enter the username

Step 5 : Create the object of the Scanner Class

Step 6 : Store the user entered username in the variable str

Step 7 : Close the scanner class to avoid memory lea

Step 8 : Apply the logic

Step 9 : Print the reversed string

Step 10 : Create reversedString method

Step 11 : Apply if condition which says if str is empty then reverse string

Step 12 : Call the function recursively 

Program :

import java.util.Scanner;

public class JavaExample2 {

    public static void main(String[] args)

    {

        String str;

        System.out.println("Enter your username:");

        Scanner sc = new Scanner(System.in);

        str = sc.nextLine();

        sc.close();

        String reversed = reverseString(str);

        System.out.println("The reversed string is:"+reversed);

    }

    public static String reverseString(String str)

    {

        if(str.isEmpty())

            return str;

        //calling function recursively

        return reverseString(str.substring(1))+str.charAt(0);

    }

}

Output :

Enter your username:

how are you doing?

The reversed string is:?gniod uoy era woh

For execution of the same do visit my Youtube Channel :

https://youtu.be/GUoz8dR5d1E

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Visit My Youtube Channel For the Cover :

https://youtu.be/kmpyEVQLuwo

Java Program To Reverse a String using Recursion

In this Java Program, we reverse a string using recursion.

The process in which the function calls itself directly or indirectly is called recursion and the corresponding function is called as recursive function

Logic :

 String reversed = reverseString(str);

Step 1 : Create obj str of String class and store the output string in it.

Step 2 : Create another object as reversed and apply the logic of the reverse string in it.

Step 3 : Output the reversed string using the System.out.println method.

Step 4 : Create reverseString method

Step 5 : Apply if statement, if str.isEmpty then return str.

Step 6 : Call function recursively.

Program :

public class JavaExample {

    public static void main(String []args)

    {

        String str = "Welcome To my Channel";

        String reversed = reverseString(str);

        System.out.println("The reversed string is : "+reversed);

    }

    public static String reverseString(String str)

    {

        if(str.isEmpty())

            return str;

        //Calling function recursively

        return reverseString(str.substring(1)) + str.charAt(0);

  }

}

Output :

The reversed string is : lennahC ym oT emocleW

For execution of the same do visit my YouTube Channel :

https://youtu.be/0XA6NlNoIQA

Java Program To Reverse a Number using Recursion

In this Java Program, we reverse a number using Recursion.

The process in which the function calls itself directly or indirectly is called recursion and the corresponding function is called as recursive function

Step 1 : Import Scanner Class

Step 2 : Create a method for reverse

Step 3 : Apply if condition in which the number should be smaller than 10

Step 4 : Print the number

Step 5 : Apply else condition in which number should mod by 10 and print the result

Step 6 : Apply reverse method condition in which number should be divided by 10

Step 7 : Create main method

Step 8 : Initialize num to 0

Step 9 : As the user to enter the number and press enter

Step 10 : Create Scanner object

Step 11 : Store the user entered number into num

Step 12 : Print Reverse of the input number is.

Step 13 : Call the reverseMethod method

Program :

import java.util.Scanner;

public class RecursionReverseDemo 

    {   

        //A method for reverse

        public static void reverseMethod(int number)

        {

            if(number < 10)

            {

                System.out.println(number);

                return;

            }

            else

            {

                System.out.print(number % 10);

                //Method is calling itself : recursion

                reverseMethod(number / 10);

            }

        }

        public static void main(String args[])

        {

            int num = 0;

            System.out.println("Input your number and press enter:");

            Scanner sc = new Scanner(System.in);

            num = sc.nextInt();

            System.out.println("Reverse of the input number is:");

            reverseMethod(num);

            System.out.println();

        }        

}

Output :

Input your number and press enter:

5678901

Reverse of the input number is:

1098765

For execution of the same do visit my YouTube Channel : 

https://youtu.be/uu50BfxfhjA

Java Program To Reverse a Number using For Loop

In this Java Program, we reverse a number using For loop.

Logic :

   for (;num != 0;)

            {

                reversenum = reversenum * 10;

                reversenum = reversenum + num%10;

                num = num/10;

            }

Step 1 : Import the Scanner Class

Step 2 :  Create the main method

Step 3 : Initialize num and reversenum equals to zero

Step 4 : Ask the user to enter the number by using System.out.println() method

Step 5 : Create Scanner object.

Step 6 : Store the captured input in num

Step 7 : Apply for loop logic to reverse the number

Step 8 : In for loop, num should be not equal to zero

Step 9 : Multiply reversenum with 10 and store its result in reversenum.

Step 10 : Add num%10 to reversenum and store the result into reversenum

Step 11 : Divide num by 10 and store the result in num.

Step 12 : Print the reversenum

Program :

import java.util.Scanner;

public class ForLoopReverseDemo 

    {

        public static void main(String args[])

        {

            int num=0;

            int reversenum = 0;

            System.out.println("Input your number and press enter:");

            //This statement will capture the user input

            Scanner sc = new Scanner(System.in);

            //Captured input would be stored in the number num

            num = sc.nextInt();

            //For loop: No initialization part as num is already initialized.

            //No increment/decrement part as logic

            //num = num/10 already decrements the value of num

            for (;num != 0;)

            {

                reversenum = reversenum * 10;

                reversenum = reversenum + num%10;

                num = num/10;

            }

         System.out.println("Reverse of specified number is:"+reversenum);                    

        }

}

Output :

Java Program To Reverse a Number using While Loop

In this Java Program, we reverse a number using while loop.

Logic :

  while (num != 0)

             {

                reversenum = reversenum * 10;

                reversenum = reversenum + num%10;

                num = num/10;                

             }

Step 1 : Import the Scanner Class

Step 2 :  Create the main method

Step 3 : Initialize num and reversenum equals to zero

Step 4 : Ask the user to enter the number by using System.out.println() method

Step 5 : Create Scanner object.

Step 6 : Store the captured input in num

Step 7 : Apply while loop logic to reverse the number

Step 8 : In while loop, num should be not equal to zero

Step 9 : Multiply reversenum with 10 and store its result in reversenum.

Step 10 : Add num%10 to reversenum and store the result into reversenum

Step 11 : Divide num by 10 and store the result in num.

Step 12 : Print the reversenum

Program :

import java.util.Scanner;

public class ReverseNumberWhile 

    {

        public static void main(String args[])

        {

            int num =0;

            int reversenum = 0;

            System.out.println("Input your number and press enter:");

            //This statement will capture the user input

            Scanner sc = new Scanner(System.in);

            //Captured input would be stored in number num

            num = sc.nextInt();

            //While loop: Logic to find out the reverse number

            while (num != 0)

             {

                reversenum = reversenum * 10;

                reversenum = reversenum + num%10;

                num = num/10;                

             }

            System.out.println("Reverse of input number is : "+reversenum);

        }

}