如何解决Java中向上造型向下造型和接口回调中的问题

public class Base {

 protected String temp = "base";
 public void fun(){
 System.out.print("BASE fun()");
 }

 public static void main(String[] args) {
 Base b =new Base();//实例化Base对象
 b.fun();   //调用父类中fun()的方法
 System.out.println(b.temp);//访问父类中的成员变量temp 
 
    /*****************************************************/ 
 System.out.println("/***************/");
 Son son = new Son();//实例化Son对象
 son.fun();  //调用son的fun方法
 System.out.println(son.temp);//访问son的成员变量temp
 
 Son S_son=new Son();    //实例化Son对象
 Base B_s =(Base)S_son;   //向上造型-----------相当于Base s =new Son();
 B_s.fun();      //调用子类的fun()方法
 System.out.println(B_s.temp);//访问父类的成员变量temp 
 
    /******************************************************/
 System.out.println("/***************/");
 Base s =new Son();//向上造型
 s.fun();     //调用子类的方法
 System.out.println(s.temp);//调用父类的成员变量temp
 
 Base ba =new Son();
 Son so = (Son)ba;      //向下造型
 so.fun();       //调用子类的fun()方法
 System.out.println(so.temp);//访问子类的成员变量temp 
 }
}
class Son extends Base{
 protected String temp = "Son";
 public void fun(){
 System.out.print("SON fun()");
 }
}

BASE fun()base
/***************/
SON fun()Son
SON fun()base
/***************/
SON fun()base
SON fun()Son

/**
 * 接口回调，和向上造型的对比
 * @author Character_Painter
 *
 */
public class Inter extends Father implements Person,Teacher{
 public void study(){
 System.out.println("学习");
 }
 public void sleep(){
 System.out.println("子类sleep()方法");
 }
 
public static void main(String[] args) {
 Father f = new Inter();
 f.sleep();//向上转型---调用
 
 Person p=new Inter();
 p.eat(); //接口回调方法
 
 Teacher t = new Inter();
 t.teach(); //接口回调方法

}

@Override
public void eat() {
 System.out.println("重写eat()方法"); 
}

@Override
public void teach() {
 System.out.println("重写teache()方法"); 
 
}

}
 
interface Person{
 public void eat();
}
interface Teacher{
 public void teach();
}
class Father{
 public void sleep(){
 System.out.println("父类sleep()方法");
 }
}

public class Thinkpad implements Electronics{

  //Thinkpad引导方法
  public void boot(){
    System.out.println("welcome,I am Thinkpad");    
  }

  //使用Thinkpad编程 
  public void program(){
    System.out.println("using Thinkpad program");
  }
}

public class Mouse implements Electronics{

  //鼠标移动
  public void move(){
    System.out.println("move the mouse");    
  }

  //鼠标点击 
  public void onClick(){
    System.out.println("a click of the mouse");
  }
}

public class Keyboard implements Electronics{

  //使用键盘输入  
  public void input(){
    System.out.println("using Keyboard input");
  }
}

import java.util.ArrayList;
import java.util.List;
public class ShopCar{

  private List mlist = new ArrayList();
  public void add(Electronics electronics){
    mlist.add(electronics);
  }

  public int getSize(){
    return mlist.size();
  }

  public Electronics getListItem(int position){
    return mlist.get(position);
  }
}

public class Test{

  public static final int THINKPAD = 0;
  public static final int MOUSE = 1;
  public static final int KEYBOARD = 2;

  public static void main(String[] args){

    //添加进购物车
    ShopCar shopcar = new ShopCar();
    shopcar.add(new Thinkpad());
    shopcar.add(new Mouse());
    shopcar.add(new Keyboard());

    //获取大小
    System.out.println("购物车存放的电子产品数量为 ——> "+shopcar.getSize());


    //开始测试thinkpad电脑
    Thinkpad thinkpad = (Thinkpad)shopcar.getListItem(THINKPAD);
    thinkpad.boot();
    thinkpad.program();

    System.out.println("-------------------");

    //开始测试Mouse鼠标
    Mouse mouse = (Mouse)shopcar.getListItem(MOUSE);
    mouse.move();
    mouse.onClick();

    System.out.println("-------------------");

    //开始测试Keyboard键盘
    Keyboard keyboard = (Keyboard)shopcar.getListItem(KEYBOARD);
    keyboard.input();
  }

}

//开始测试thinkpad电脑
Thinkpad thinkpad = (Thinkpad)shopcar.getListItem(THINKPAD);
thinkpad.boot();
thinkpad.program();