How to determine whether a number is prime in java

What are prime numbers?

Prime numbers are also called prime numbers, and there are infinite numbers. A prime number is defined as a natural number greater than 1 that has no other factors except 1 and itself. Such a number is called a prime number.

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Purpose:

Judge whether a number is a prime number

Judgment idea:

1. First, use the Math.sqrt() function to square the number, such as [Math.sqrt(n)];

2. Then use the for loop and if statement to make the remainder judgment. That’s it.

Specific example:

import java.util.Scanner;
public class TestWork {
	public static void main(String[] args) {
		boolean isPrime = true;
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入一个正整数");
		int num = sc.nextInt();
		if (num > 0) {
			int k = (int) Math.sqrt(num);//k为num的正平方根，取整数
			for (int i = 2; i <= k; i++) {
				if (num % i == 0) {
					isPrime = false;//不是素数
					break;
				}
			}
		}
		if (isPrime) {
			System.out.println(num + "是素数");
		} else {
			System.out.println(num + "不是素数");
		}
	}
}

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