# JAVA PROGRAM TO FIND PRIME NUMBERS

PRIME NUMBER : Prime numbers are the numbers that are divisible by 1 and itself and must be greater than 1. For Example, 11 is a prime number since it is only divisible by 1 and itself (11). 0 and 1 are not considered as prime numbers moreover 2 is only even prime number since it is also divisible by 1 and itself (2) and all other even numbers are divisible by 2, so they are not considered as prime.

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• Java Program to check if a number is prime or not
• Java Program to find prime numbers between two numbers
• Java Program to find prime numbers between two numbers(Another way)
• Java Program to find prime numbers between 1 to 100
• Java Program to check if a number is prime or not using while loop

### Example 1 : Java Program to to check if a number is prime or not ``````// Java Program to to check if a number is prime or not
import java.util.Scanner;
class PrimeDemo {
public static void findprime(int num) {
boolean flag = true;
if (num <= 1) {
flag = false;
}
else {
for (int i = 2; i <= num / 2; i++) { // non-prime condition
if (num % i == 0) {
flag = false;
break;
}
}
}
if (flag) {
System.out.println(num + " " + "is a prime number");
} else {
System.out.println(num + " " + "is not a prime number");
}
}
}

public class Codebator {
public static void main(String[] args) {
System.out.println("Enter any Number");
Scanner sc = new Scanner(System.in);
int num = sc.nextInt();
PrimeDemo.findprime(num); //calling static method
}
}
``````

#### OUTPUT :

`Enter any Number17 17 is a prime number `
• The findprime(int num) static method is used to check if the parameter passed to it is a prime number or not. In our case the number is 17.

• Check if a number is a natural number or not. Natural Numbers are all positive integers from 1 to infinity and are mainly used for counting purpose.

• Perform Division operation if number is not less than 1 or equal to 1.

• If remainder is 0 then return false and break the loops, it means number is not a prime number.

• If remainder is non-zero then return true , it means number is a prime number.

### Example 2 : Java Program to to find prime numbers between two numbers

Lets make the use of our previous prime number method findprime(num) to find out prime numbers between two given numbers; ``````// Java Program to to find prime numbers between two numbers
import java.util.Scanner;
class PrimeDemo {

public static void checkprime(int first,int last) {
for(int i=first;i<=last;i++) {
findprime(i);
}
}

public static void findprime(int num) {
boolean flag = true;
if (num <= 1) {
flag = false;
}
else {
for (int i = 2; i <= num / 2; i++) { // non-prime condition
if (num % i == 0) {
flag = false;
break;
}
}
}
if (flag) {
System.out.print(num+" ");
}
}
}

public class Codebator {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter first Number");
int first = sc.nextInt();
System.out.println("Enter second Number");
int last=sc.nextInt();
PrimeDemo.checkprime(first,last); //calling static method
}
}
``````

#### OUTPUT :

`Enter first Number78 Enter second Number 93 79 83 89 `
• The checkprime(first,last) static method accepts two parameters, which are used to find prime numbers between two numbers.

• Use the same method findprime(int num) as in the above program to find the prime numbers between two numbers.

### Example 3 : Java Program to to find prime numbers between two numbers(Another way) ``````// Java Program to to find prime numbers between two numbers
import java.util.Scanner;
class PrimeDemo {

public static void checkprime(int first,int last) {
for(int i=first;i<=last;i++) {
if(findprime(i)) {
System.out.println(i);
}
}
}

public static boolean findprime(int num) {
if (num <= 1) {
return false;
}
else {
for (int i = 2; i <= num / 2; i++) { // non-prime condition
if (num % i == 0) {
return false;
}
}
}
return true;
}
}

public class Codebator {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter first Number");
int first = sc.nextInt();
System.out.println("Enter second Number");
int last=sc.nextInt();
PrimeDemo.checkprime(first,last); //calling static method
}
}
``````

#### OUTPUT :

`Enter first Number78 Enter second Number 93 79 83 89 `

### Example 4 : Java Program to to find prime numbers between 1 to 100 ``````// Java Program to to find prime numbers between 1 to 100.
import java.util.Scanner;
class PrimeDemo {

public static void checkprime(int num) {
for(int i=0;i<=num;i++) {
if(findprime(i)) {
System.out.println(i);
}
}
}

public static boolean findprime(int num) {
if (num <= 1) {
return false;
}
else {
for (int i = 2; i <= num / 2; i++) { // non-prime condition
if (num % i == 0) {
return false;
}
}
}
return true;
}
}

public class Codebator {
public static void main(String[] args) {
int num=100;
PrimeDemo.checkprime(num); //calling static method
}
}
``````

#### OUTPUT :

`2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 `

### Example 5 : Java Program to to check if a number is prime or not using while loop ``````// Java Program to to check if a number is prime or not using while loop
import java.util.Scanner;
class PrimeDemo {
public static void findprime(int num) {
int i=2;
boolean flag = true;

if(num<=1) {
flag=false;
}

while(i<=num/2) {
if(num%i==0) {
flag=false;
break;
}
i++;
}
if (flag) {
System.out.println(num + " " + "is a prime number");
} else {
System.out.println(num + " " + "is not a prime number");
}
}
}

public class Codebator {
public static void main(String[] args) {
System.out.println("Enter any Number");
Scanner sc = new Scanner(System.in);
int num = sc.nextInt();
PrimeDemo.findprime(num); //calling static method
}
}
``````

#### OUTPUT :

`Enter any Number23 23 is a prime number `