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In this tutorial, we will write a program to check whether the number is prime or not in java. Before that, you should have knowledge on the following topic in java.

• for loop
• if statement

Prime Number

A number is said to be a prime number if it is divisible by itself and 1. Example: 3, 5, 7, 11, 13, 17, 19, etc.

Explanation:
We take a boolean variable isPrime and assigned it to be true. Then we take the user input and start a for loop for i = 2 end the loop for i less than half of the number entered. i will increase by 1 after each iteration.

Inside for loop, a temp variable will contain the remainder of each iteration. And then if statement will check for temp to be 0 that is if the remainder is zero, isPrime is set to false. If isPrime is true, the number is Prime number else not.

Java Program to check whether a Number is Prime or Not

source code: Java Program to check for the prime number.

 //check for the prime Number

 import java.util.Scanner;
 public class PrimrNumberCheck
 {
   public static void main(String args[])
   {
     int temp;
     boolean isPrime = true;
     Scanner scan = new Scanner(System.in);

     System.out.print("Enter any number: ");

     int num = scan.nextInt();
     scan.close();

     for (int i = 2; i <= num / 2; i++)
     {
       temp = num % i;
       if (temp == 0)
       {
         isPrime = false;
         break;
       }
     }

     if (isPrime)
       System.out.println(num + " is a Prime Number"); //If isPrime is true 
     else
       System.out.println(num + " is not a Prime Number"); //If isPrime is false 
   }
 }

Output:

Enter any number: 13
13 is a Prime Number

In this tutorial, we will write a Java Program to check Armstrong number. We will write two different programs to check the armstrong number in java.

1. What is an Armstrong number?
2. Java program to check the Armstrong Number(for any digit number) using a while and for.
3. Java program to check the Armstrong Number(using Math.pow() method).

What is an Armstrong Number?

A number is said to be an Armstrong Number if even after the sum of its digits, where each digit is raised to the power of the number of digits is equal to the original number. For example 153, 371, 407, 9474, etc are Armstrong Numbers.

Follow the below calculation.

Java program to check the Armstrong Number using while and for loops

import java.util.Scanner;
 
 public class ArmstrongNumber
 {
  public static void main(String[] args)
  {
    int n, num, totalDigits, remainder, result = 0;
 
    System.out.println("Enter the Number:");
    Scanner scanner = new Scanner(System.in);
    
    n = scanner.nextInt();
    scanner.close();
    
    //setting the power to the no. of digits
    totalDigits = String.valueOf(n).length();
    
    num = n;
 
    while (num != 0)
    {
        remainder = num % 10;
        int lastDigits = 1;
        
        for(int i = 0; i < totalDigits; i++)
         {
           lastDigits = lastDigits * remainder;
         }
         
        result = result + lastDigits;
        num /= 10;
    }
 
    if(result == n)
        System.out.println(n + " is an Armstrong number.");
    else
        System.out.println(n + " is not an Armstrong number.");
  }
 }

Output: You can check for any digit Number.

Enter the Number:
9474
9474 is an Armstrong number.

Explanation:
First we create required variables(n, num, totalDigits, remainder, result). Get User Input and store it in n, then we need the number of digits present in that number and store it n totalDigits using code (totalDigits = String.valueOf(n).length();). After that, copy the entered number to num.

Now start the while loop checking num is not equal to zero. While stops as soon as num becomes zero.
After each iteration of the while loop, the last digit of num is stored in remainder for the second use. We initiate an int variable lastDigits = 1.

Now the for loop runs until the totalDigits less than i where is initiated as 0 and increase by 1 after each iteration. Inside for loop lastDigits is multiplied to remainder and the result is added to lastDigits.

After the end of for loop, the value of lastDigits is assigned to the result variable.
and at the end, we divide the num by 10 i.e num /= 10; which will remove the last digit from the number.
This step is continued until the num becomes 0.

At last, we will check with if-else statement whether the result is equal to the original number or not. If it is found equal,l then the entered number is an Armstrong Number.

Java program to check the Armstrong Number using Math.pow() method

 //check for armstrong number
  
import java.util.Scanner;
 
 public class ArmstrongNumber
 {
  public static void main(String[] args)
  {
    int n, num, power, remainder, result = 0;
 
    
    System.out.print("Enter the Number: ");
    Scanner scanner = new Scanner(System.in);
    
    n = scanner.nextInt();
    scanner.close();
    
    //seting the power to the no. of digits
    power = String.valueOf(n).length();
    
    num = n;
 
    while (num != 0)
    {
        remainder = num % 10;
        result += Math.pow(remainder, power);
        num /= 10;
    }
 
    if(result == n)
        System.out.println(n + " is an Armstrong number.");
    else
        System.out.println(n + " is not an Armstrong number.");
  }
 }

Output: You can check for any digit Number.

Enter the Number: 370
370 is an Armstrong number

Explanation: In the above program we use the inbuilt method (Math.pow()) which makes it easy for us to calculate the raised power to the number.

The process is the same as explained above, only the difference is instead of for loop we use the method(Math.pow()) as result += Math.pow(remainder, power);.

If we were to calculate for the only three-digit number then we can simply replace the code:
result += Math.pow(remainder, power); with
result = result + remainder*remainder*remainder;

In this java program tutorial, we will write a java program to display the Fibonacci series. Let us first understand what is Fibonacci series is and then the Java program to generate them.

What is Fibonacci Series?

Fibonacci series is the series of numbers where the next number is achieved by the addition of the previous two numbers. The initial addition of two numbers is 0 and 1.

For example: 0,1,1,2,3,5,8,13….etc.

We will see two ways to print the Fibonacci Series.

• With the help of iteration(for-loop).
• Using recursion.

Program Explanation:
First, we need to initialize the two terms as 0 and 1 as a = 0, b = 0; then get user input for the total number of elements in a series which is stored in an integer variable n.

After that start iteration up to the number of elements the user inputs. Inside for loop, we assigned the b value in a and the sum value in b and the sum is the addition of a and b. Then we print the value at every iteration as shown in a program.

At last, the program exits the iteration when integer i is less than or equal to the number of elements as,
i <= n.

1. Java program to display Fibonacci series using for loop

//Fibonacci series in java

import java.util.Scanner;

public class FibonacciJava
{
  public static void main(String[] args)
  {
    int n, a = 0, b = 0, sum = 1;

    Scanner s = new Scanner(System.in);

    System.out.print("Enter the Number:");
    n = s.nextInt();

    System.out.print("Fibonacci Series of entered number are:");
    for (int i = 1; i <= n; i++)	//display
    {
      a = b;
      b = sum;
      sum = a + b;
      System.out.print(a + " ");
    }
  }
}

Output:

Enter the Number:6
Fibonacci Series of entered number are:0 1 1 2 3 5

2. Fibonacci series using Recursion in java

//Fibonacci Using Recursion

import java.util.Scanner;
public class FiboSeries
{
    public static int fiboRecursion(int n)
    {
     if(n == 0)
     {
       return 0;
     }
     if(n == 1 || n == 2)
     {
       return 1;
     }
     return fiboRecursion(n-2) + fiboRecursion(n-1);
    }
	
  public static void main(String args[]) 
  {
    int number;
    Scanner s = new Scanner(System.in);
        
    System.out.print("Enter the Number:");
    number = s.nextInt();
        
    System.out.print("Fibonacci Series of entered number: ");
	
    for(int i = 0; i < number; i++)
    {
	System.out.print(fiboRecursion(i) +" ");
    }
  }
}

After executing, the following output will be obtained.

Enter the Number:8
Fibonacci Series of entered number: 0 1 1 2 3 5 8 13