lab5打卡

PART I：

最后一问其实没太看懂。。

package lab5;

public class Tester{
    public Tester(){
    }
    public void test() {
        System.out.println("test!");
    }
    public static void main(String[] args) {
        Tester X=new Tester();
        Tester2 Y=new Tester2();
        X=Y;        
      //Y=X;  //compile-time error;
        Y=(Tester2)X;
        X=new Tester();
      //Y=(Tester2)X;//runtime error;
/**********************************************************/
        Tester[] xa;
        Tester2[] ya=new Tester2[2];
        xa=ya;
      //ya=xa; //compile-time error; 
/**********************************************************/
        ya=new Tester2[2];
        ya=(Tester2[])xa;
        xa=ya;
/**********************************************************/
        xa=new Tester[2];
        xa[0]=new Tester();
        xa[1]=new Tester();
        xa[0]=ya[0];
      //ya[0]=xa[0]; //compile-time error;
      //ya=(Tester2[])xa;//runtime error;
    }
     
}

PART II:

package lab5;

public class T3 extends Tester implements T0{
      T3(){         
      }
      public static void main(String[] args) {
          Tester shh=new T3();
          T3 hihi=new T3();
          shh.test();
          hihi.test();
      }
}

package lab5;

public interface T0 {
    public void test();
}

(a)YES

(b)NO

(c)NO

(d)YES

 PART III：

PART IV:

(a)    It will call the subclass method

(b)    run-time error、

（c）