switch多选择结构

public class switchDemo01 {
    public static void main(String[] args) {
        //case 穿透
        Scanner grade = new Scanner(System.in);
        System.out.println("请输入>>:");
        String a = grade.next();
        switch (a){     //匹配一个值
            case "A":
                System.out.println("大写NB");
                break;  //可选，没写break case穿透了
            case "B":
                System.out.println("小写nb");
                break;
            case "C":
                System.out.println("一般nb");
                break;
            default:   //可选
                System.out.println("未知等级");
                break;
            case "D":
                System.out.println("dd");
        }
        grade.close();
    }
}

switch case bleak default