As we know that a number is a prime number if it is a natural number greater than 1 and it can be divided either by 1 or by the number itself. As example - 2, 3, 5, 7, 11, 13, 17 ….
If you take any number and check if it has any divisor you will find that by going that number/2 digits starting from 2 it will have a divisor, if one exists.
As example if number is 8 then you just need to check till 4 to see if it divides by any number or take 15 you just need to check till 7 to see if it divides completely by any number. We'll use the same logic to write our program to check for prime number.
Java program
import java.util.Scanner;
public class PrintPrime {
public static void main(String[] args) {
// take input from the user
Scanner sc = new Scanner(System.in);
System.out.println("Enter number till which prime numbers are to be printed - ");
int num = sc.nextInt();
for(int i = 2; i <= num; i++){
if(isPrime(i)){
System.out.print(i + " ");
}
}
}
private static boolean isPrime(int num){
boolean flag = true;
// loop from 2, increment it till number/2
for(int i = 2; i < num/2; i++){
// no remainder, means divides
if(num % i == 0){
flag = false;
break;
}
}
return flag;
}
}
Output
Enter number till which prime numbers are to be printed -
50
2 3 4 5 7 11 13 17 19 23 29 31 37 41 43 47
Here scanner class is used to get input from the user.
- Refer How to read input from console in Java? to see other ways to get input from user.
That's all for this topic Displaying prime numbers - Java program. If you have any doubt or any suggestions to make please drop a comment. Thanks!
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