# Java program to check whether number is prime or not

Let’s learn java program to check whether number is prime or not.

## Java program to check whether number is prime or not

Prime number program in java is one of the most asked interview question.

A prime number is a number that is greater than one and divided by one or itself.

Also read – palindrome number program in java

Prime numbers are those numbers which cannot be divided by other numbers than 1 or itself.

Example : 2, 3, 5, 7, 11, 13, 17….

Here’s the java program to check whether number is prime or not.

```public class PrimeNumberInJava
{
public static void main(String[] args)
{
int a, b = 0, flag = 0;
int number = 66;
b = number / 2;
if(number == 0 || number == 1)
{
System.out.println(number + " is not prime number");
}
else
{
for(a = 2; a <= b; a++)
{
if(number % a == 0)
{
System.out.println(number + " is not prime number.");
flag = 1;
break;
}
}
if(flag == 0)
{
System.out.println(number + " is prime number.");
}
}
}
}

```

Output:

prime number program in java using while loop

Similarly let’s see prime number program in java using while loop.

```import java.util.Scanner;
{
public static void main(String[] args)
{
boolean checkPrime = true;
Scanner sc = new Scanner(System.in);
int number = sc.nextInt();
int a = 2;
while(a <= number / 2)
{
if(number % a == 0)
{
checkPrime = false;
break;
}
a++;
}
if(checkPrime)
{
System.out.println(number + " is a prime number.");
}
else
{
System.out.println(number + " is not a prime number.");
}
sc.close();
}
}

```

Output:

17 is a prime number.

print first 10 numbers prime numbers in java

Now let’s see print first 10 prime numbers in java.

```public class FirstTenPrimeNumbers
{
public static void main(String[] args)
{
int count = 0, number = 0, a = 1, b = 1;
while(number < 10)
{
b = 1;
count = 0;
while(b <= a)
{
if(a%b == 0)
count++;
b++;
}
if(count == 2)
{
System.out.printf("%d ", a);
number++;
}
a++;
}
}
}

```

Output:

2 3 5 7 11 13 17 19 23 29

NOTE: 2 is the only even prime number. 0 and 1 are not prime numbers.

java program to print prime numbers in a given range

Now let’s learn java program to print prime numbers in a given range.

```public class PrimeNumberRangeDemo
{
public static void main(String[] args)
{
int lowerRange = 10, higherRange = 50;
while(lowerRange < higherRange)
{
boolean flag = false;
for(int a = 2; a <= lowerRange / 2; ++a)
{
if(lowerRange % a == 0)
{
flag = true;
break;
}
}
if(!flag && lowerRange != 0 && lowerRange != 1)
System.out.print(lowerRange + " ");
++lowerRange;
}
}
}

```

Output:

11 13 17 19 23 29 31 37 41 43 47

### print numbers upto n in java

Here let’s learn java program to print prime numbers upto n.

```import java.util.Scanner;
public class PrimeUptoN
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
int a = 0;
int n = 0;
String strPrime = "";
System.out.println("Please enter the value of n: ");
int number = sc.nextInt();
for(a = 1; a <= number; a++)
{
int counter = 0;
for(n = a; n >= 1; n--)
{
if(a % n == 0)
{
counter = counter + 1;
}
}
if(counter == 2)
{
strPrime = strPrime + a + " ";
}
}
System.out.println("prime numbers upto n are: ");
System.out.println(strPrime);
sc.close();
}
}

```

Output:

Please enter the value of n: 10
prime numbers upto n are: 2 3 5 7

Please enter the value of n: 50
prime numbers upto n are: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

prime number program in java using scanner

Let’s learn prime number program in java using scanner.

Here’s the java program to check whether number is prime or not.

```import java.util.Scanner;
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
System.out.println("Please enter a number to check prime number: ");
int number = sc.nextInt();
{
System.out.println(number + " is a prime number");
}
else
{
System.out.println(number + " is not a prime number");
}
sc.close();
}
{
if(number <= 1)
{
return false;
}
for(int a = 2; a < Math.sqrt(number); a++)
{
if(number % a == 0)
{
return false;
}
}
return true;
}
}

```

Output:

Please enter a number to check prime number: 15
15 is not a prime number

Please enter a number to check prime number: 19
19 is a prime number

java program to print prime numbers from 2 to n

Now let’s learn java program to print prime numbers from 2 to n. Here we create checkPrime() method.

In checkPrime() method we have for loop from 2 to number/2.

Here if number divides by some number between 2 to (number/2)-1 then number will not be prime.

Let’s see java program to check whether number is prime or not.

Here’s java program to print prime numbers from 2 to n.

```import java.util.Scanner;
{
public static void main(String[] args)
{
int loop, num;
System.out.println("Please enter value of n: ");
Scanner sc = new Scanner(System.in);
num = sc.nextInt();
for(loop = 2; loop < num; ++loop)
{
if(checkPrime(loop))
{
System.out.println(loop);
}
}
sc.close();
}
public static boolean checkPrime(int number)
{
int a;
boolean boolPrime = true;
for(a = 2; a < number / 2; a++)
{
if(number%a == 0)
{
boolPrime = false;
break;
}
}
return boolPrime;
}
}

```

Output:

Please enter value of n: 20
2
3
4
5
7
11
13
17
19

Please enter value of n: 30
2
3
4
5
7
11
13
17
19
23
29