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javafor-loopmethodsoperators
Abdelillah
Abdelillah

Reputation: 119

Can someone help me to understand this for loop?

Hello i'm new learner at java, the tutor on Udemy gave us this method but he didn't explain it, i found it hard to understand, and i tried to execute it, but still the same thing. PS : sorry for my English i'm Arabian. This is the method:

public static boolean isPrime(int n) {

    if(n == 1) {
        return false;
    }

        for(int i = 2; i <= n/2; i++) {
            if(n % i == 0) {
                return false;
            }
        }

    return true;


}

Upvotes: 0

Views: 59

Answers (2)

Mathias Dam
Mathias Dam

Reputation: 107

The method isPrime(int n) takes an integer n and checks whether it is prime or not.

First it checks whether n is equal to 1. If it is the method returns false, because 1 is not prime.

Afterwards it loops through all the numbers between 2 and n/2, and checks if n is divisible by that number. If it is, the method returns false because then it is not prime.

The reason why it does not check every number from 2 til n is because it would be redundant. The number n can never be expressed as a product of a whole number and a number that is bigger than n/2, except n but then it would not be a prime number.

Upvotes: 0

Nick Nikolov
Nick Nikolov

Reputation: 261

The code loops through all numbers from 2 to n/2 and checks if n is divisible by that number. If it is divisible by any of these numbers the function returns false as n has a divisor. If we have found no divisor from 2 to n/2 the number is prime. A better approach would be to loop to the square root of n.

Upvotes: 2

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