编写java程序模拟中国人、美国人是人，北京人是中国人，完成相应类别人群的基本信息输出。除主类外，程序中还有4 个类：People、ChinaPeople、AmericanPeople 和BeijingPeople 类。要求如下：  People 类有权限是protected 的double 型成员变量height 和weight，以及public void speakHello()、public void averageHeight()和public void averageWeight()方法。

以下是相应的Java代码：

public class People {
    protected double height;
    protected double weight;
    
    public void speakHello() {
        System.out.println("Hello!");
    }
    
    public void averageHeight() {
        System.out.println("The average height of people is " + height + " cm.");
    }
    
    public void averageWeight() {
        System.out.println("The average weight of people is " + weight + " kg.");
    }
}

public class ChinaPeople extends People {
    public ChinaPeople() {
        height = 170.0;
        weight = 65.0;
    }
}

public class AmericanPeople extends People {
    public AmericanPeople() {
        height = 180.0;
        weight = 75.0;
    }
}

public class BeijingPeople extends ChinaPeople {
    public BeijingPeople() {
        height = 173.0;
        weight = 68.0;
    }
}

public class Main {
    public static void main(String[] args) {
        People p1 = new ChinaPeople();
        People p2 = new AmericanPeople();
        People p3 = new BeijingPeople();
        
        p1.speakHello();
        p1.averageHeight();
        p1.averageWeight();
        
        p2.speakHello();
        p2.averageHeight();
        p2.averageWeight();
        
        p3.speakHello();
        p3.averageHeight();
        p3.averageWeight();
    }
}

在上面的代码中，我们定义了一个People类，它有两个protected成员变量height和weight，以及三个public方法speakHello()、averageHeight()和averageWeight()。

然后，我们定义了三个子类ChinaPeople、AmericanPeople和BeijingPeople，它们都继承自People类，并且在构造函数中为height和weight赋值。

最后，在主类Main中，我们创建了三个不同的People类型的实例，并调用它们的方法输出相应的基本信息。