编写一个主类，主类中含有四个类，

/*编写一个java应用程序，程序中有四个类：People，ChinaPeople，AmericanPeople，BeijingPeople，
people类有访问权限是protected的double类型的weight和height以及public void speakHello();
public void averageHeight(),public void averageWeight()方法。
Chinapeople类是people的子类，新增public void gongfu()方法，以及重写public void speakHello();
public void averageHeight(),public void averageWeight()方法。
Americanpeople类是people的子类，新增 public void americanBoxing(),
以及重写public void speakHello();
public void averageHeight(),public void averageWeight()方法。
BeijingPeople类是Chinapeople的子类，新增 public void Opera(),
以及重写public void speakHello();public void averageHeight(),
public void gongfu()方法,public void averageWeight()方法。*/
     class People{
         protected double height;
         protected double weight;
         public void speakHello(){
             System.out.println("hello");
         }
         public void averageHeight(){}
         public void averageWeight(){}
     }
     class AmericanPeople extends People{
         public void speakHello(){
             System.out.println("american i");
         }
         public void averageHeight(){}
         public void averageWeight(){}
         public void americanBoxing(){}
     }
     class ChinaPeople extends People{
         public void speakHello(){
             System.out.println("china hi");
         }
         public void averageHeight(){}
         public void averageWeight(){}
         public void chinaGongfu(){}
         
     }
     class BeijingPeople extends ChinaPeople{
         public void speakHello(){
             System.out.println("BEIJING HI");
         }
         public void averageHeight(){}
         public void averageWeight(){}
         public void chinaGongfu(){}
         public void beijingOpera(){}
         
     }
     public class Alei {
         public static void main(String []args){
            //创建 子类AmericanPeople的一个实例对象，使用默认构造法
             AmericanPeople a=new AmericanPeople();
             //方法重写
             a.speakHello();
             a.averageHeight();
             a.averageWeight();
            //创建子类ChinaPeople的一个实例对象，使用默认构造法
             ChinaPeople b=new ChinaPeople();
             //方法重写
             b.speakHello();
             b.averageHeight();
             b.averageWeight();
             //创建子类BeijingPeople的实例对象，使用默认构造法
             BeijingPeople c=new BeijingPeople();
             //方法重写
             c.speakHello();
             c.averageHeight();
             c.averageWeight();
             c.chinaGongfu();
}
}

运行结果如下：

american i
china hi
BEIJING HI