Prime number in java: Algorithm and Programs

What is a prime number in Java?

A prime number in java is a number that is greater than 1 and divided by 1 or itself only. or we can say that a prime number can be divided by 1 or itself.

A number greater than 1 that is not prime is called a composite number.

for example:- 7 is a prime number because 7*1=7 or 1*7=7.

2=1,2 it is prime

3=1,2 it is prime

4=1,2,4 it is not prime

5=1,5 it is prime

6=1,2,3,6 it is not prime

Algorithm of prime number

simple steps of prime number:-

START
Step 1 → Take integer variable num
Step 2 → Divide the variable num with (num-1 to 2)
Step 3 → If num is divisible by any value (num-1 to 2)  not prime
Step 4 → Else it is prime
STOP

Prime Number in java using a for loop

public class Main {

  public static void main(String[] args) {

    int a = 11;
    boolean flag = false;
    for (int loop = 2; loop <= a / 2; ++i) {
      // condition for nonprime number
      if (a % loop == 0) {
        flag = true;
        break;
      }
    }

    if (!flag)
      System.out.println(a + " is a prime number.");
    else
      System.out.println(a + " is not a prime number.");
  }
}

 Output

 

11 is a prime number

Prime Number in java using a while loop

 

public class Main {

  public static void main(String[] args) {

    int a = 11, loop = 2;
    boolean flag = false;
    while (loop <= a / 2) {
      // condition for nonprime number
      if (a % loop == 0) {
        flag = true;
        break;
      }

      ++loop;
    }

    if (!flag)
      System.out.println(a + " is a prime number.");
    else
      System.out.println(a + " is not a prime number.");
  }
}

Output

 

11 is a prime number 

Prime Number in Java using Scanner

import java.util.Scanner;

import java.util.Scanner;

public class Prime {

public static void main(String[] args) {

Scanner s = new Scanner(System.in);

System.out.print(“Enter a number : “);

int num = s.nextInt();

if (isprime(num)) {

System.out.println(“it is a prime number”);

}

       else {

System.out.println(” it is not a prime number”);

}

}

 

public static boolean isprime(int num) {

if (num <= 1) {

return false;

}

for (int loop = 2; loop < Math.sqrt(num); loop++) {

if (num % loop == 0) {

return false;

}

}

return true;

}

}

Output

Enter the number : 3
it is a prime number

 

For Fibonacci series Algorithm and programs click here

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