求质数并打印，下面是我的写法，求改进，求其他写法

Question

package test;
import java.util.Scanner;

public class TestPrime {

public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    System.out.println("请输入一个整数");
    int num=sc.nextInt();
    System.out.println("所求素数范围是 2-"+num);

    int index=0; //够10个换行输入
    for(int i=2;i<=num;i++){

        if(i<=7){
            switch(i){
            case 2:
                System.out.print(i+" ");
                index++;
                break;
            case 3:
                System.out.print(i+" ");
                index++;
                break;
            case 5:
                System.out.print(i+" ");
                index++;
                break;
            case 7:
                System.out.print(i+" ");
                index++;
                break;
            }
        }else{
            if(i%2==0 || i%3==0 || i%5==0 || i%7==0){
                continue;
            }
            else{
                System.out.print(i+" ");
                index++;
                if(index%10==0){
                    System.out.println();
                }
            }


        }
    }



}

}

Answer 1

 for(int i=2;i<=num;i++)
{
    for(int j=2;j<i;j++)
    {
        if(i%j==0 ) break;
    }
    if(j>=i)
    {
        System.out.print(i+" ");
        index++;
        if(index%10==0)
        {
            System.out.println();
        }
    }
}