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Java program to check for prime and find next Prime in Java
Any whole number which is greater than 1 and has only two factors that is 1 and the number itself, is called a prime number. Other than these two number it has no positive divisor. For example: 7 = 1 × 7
Following is the algorithm to find whether a number is prime or not −
Take integer variable A.
Divide the variable A with (A-1 to 2).
If A is divisible by any value (A-1 to 2) it is not prime.
Else it is prime.
Example
Following Java program accepts an integer from the user, finds whether the given number is prime and, prints the next prime number.
import java.util.Scanner;
public class NextNumberisPrime {
public static int isPrime(int num){
int prime = 1;
for(int i = 2; i < num; i++) {
if((num % i) == 0) {
prime = 0;
}
}
return num;
}
public static int nextPrime(int num) {
num++;
for (int i = 2; i < num; i++) {
if(num%i == 0) {
num++;
i=2;
} else {
continue;
}
}
return num;
}
public static void main(String args[]){
Scanner sc = new Scanner(System.in);
System.out.println("Enter a number ::");
int num = sc.nextInt();
int result = 0;
int prime = isPrime(num);
if (prime == 1) {
System.out.println(num+" is a prime number");
} else {
System.out.println(num+" is not a prime number");
}
System.out.println("Next prime number is: "+nextPrime(num));
}
}Output
Enter a number :: 25 25 is not a prime number Next prime number is: 29
Updated on: 10-Oct-2019
5K+ Views
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