输出n~m所有质数

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt(), m = input.nextInt();
        for (int i = n; i <= m; i++) {
            boolean flag = true;
            if (i == 1) {
                flag = false;
            }
            for (int j = 2; j < i; j++) {
                if (i % j == 0) {
                    flag = false;
                }
            }
            if (flag) {
                System.out.println(i);
            }
        }

    }
}

优化

for (int i = n; i <= m; ++i) {
    if (i == 1) {
        continue;
    }
    boolean flag = true;
    for (int j = 2; j < i; ++j) {
        if (i % j == 0) {
            flag = false;
        }
    }
    if (flag) {
        System.out.println(i);
    }
}