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.
Table of Contents
[hide]- 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
