java基础-for循环、while循环相关

public class Example1 {
    public static void main(String[] args) {

        // 乘法口诀表
        String a = "";
        for(int i = 1 ; i <= 9 ; i ++){
            for(int j =1; j <= 9 ; j++){
                if(j == 1){
                    a+= "\n";
                }
                if(i < j) continue;
                a+=  ""+i +"*"+ j + "=" +i*j +"\t";
            }
        }
        System.out.println(a);
    }
}

public class Example2 {
    public static void main(String[] args) {
        //使用while实现 1+1/2！+1/3！+1/4！ + ... + 1/20！
        double Sum = 0;

        int i = 1 ;
        while(i<21){
            double a = 1;
            int j = i;
            // 算分母
            while(j>0){
                a *= j;
                j--;
            }
            double b = 1/a;

            Sum += b;
            i++;
        }
        System.out.println(Sum);
    }
}