Java determines whether number is prime

There are several ways to determine whether a number is a prime number:

(1)Use between 2 and number-1 All numbers are divided by number. If one is divisible, it means that number is a non-prime number; unless all numbers are not divisible, it means that number is a prime number.                                                                                                                                                                                                                                                                                                       # Prime number; unless all numbers are not divisible, the number is prime. (3) Use all numbers between 2 and the square root of number to divide number. If any number can be divided evenly, it means that number is a non-prime number; unless all numbers cannot be divided evenly, it means that number is a prime number. .

The efficiency of these three methods is gradually improved. The implementation of the third method is listed below:

import java.util.Scanner;
public class Test2 {
    public static void main(String[] args) {
        int number; // 输入的数字
        Scanner input = new Scanner(System.in);
        System.out.println("请输入数字");
        number = input.nextInt(); // 输入数字
        if(isPrimeNumber(number)){
            System.out.println(number + "是一个素数");
        }
        else{
            System.out.println(number + "是一个非素数");
        }
    }
    public static boolean isPrimeNumber(int num){
        if(num < 2){
        System.out.println("数据错误");
        return false;
    }
    int k = (int)Math.sqrt(num); //num的平方根
    int i;
    for(i=2; i<=k; i++){ //依次用2..k之间的数去整除num，如果没有一个数能被整除，说明num是素数
        if(num % i == 0){
            break;
        }
    }
    if(i > k){
        return true;
    }
        return false;
    }
}

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