对象向上、向下转型

class Father {

    public void tell() {
        System.out.println("Father tell");
    }
}

class Son extends Father {

    public void tell() {
        System.out.println("Son tell");
    }
}

public class Demo {
    public static void main(String args[]) {
        //向下转型
        Father father = new Son();
        father.tell();
        //向上转型（向上转型时要先进行向下转型）
        Father father = new Son();
        Son son = (Son) father;
        son.tell();

    }
}