Java中容易被遗忘的default关键字

int day = 8;
String dayString;
switch (day) {
    case 1: dayString = "Monday";
            break;
    case 2: dayString = "Tuesday";
            break;
    case 3: dayString = "Wednesday";
            break;
    case 4: dayString = "Thursday";
            break;
    case 5: dayString = "Friday";
            break;
    case 6: dayString = "Saturday";
            break;
    //如果case没有匹配的值，那么肯定是星期日
    default: dayString = "Sunday";
             break;
}
System.out.println(dayString);

interface IntefercaeDemo {

    //具体方法
    default void showDefault(){
        System.out.println("this is showDefault method");
    }
    //具体方法
    static void showStatic(){
        System.out.println("this is showStatic method");
    }

    //没有实现的抽象方法
    void sayHi();
}
class LearnDefault implements IntefercaeDemo{
    //实现抽象方法
    @Override
    public void sayHi() {
        System.out.println("this is sayHi mehtod");
    }

    public static void main(String[] args) {
        //接口中被static所修饰的具体方法
        IntefercaeDemo.showStatic();

        //将实现了IntefercaeDemo的类实例化
        LearnDefault learnDefault = new LearnDefault();
        //被Default所修饰的具体方法可以通过引用变量来调用
        learnDefault.showDefault();

    }
}

public class Demo{
    // 没有访问修饰符修饰，访问限制等级为default
    String name;
    void show(){}
}