test7.3 &7.4

没有搞明白7.4什么意思，代码跟书上一样，就是省略了Cartoon的构造器看看基类还能不能构造

class Art

{Art(){System.out.println("Art constructor");}}

class Drawing extends Art

{Drawing(){System.out.println("Drawing constructor");}}

public class Cartoon extends Drawing{
//Cartoon(){System.out.println("Cartoon constructor");}
public static void main(String[] args) {
Cartoon x=new Cartoon();
}

}