编写一个Java应用程序，除了主类外，该程序中还有4个类：People、ChinaPeople、AmericanPeople和BeijingPeople。要求如下：  People类有访问权限是protected的double型成员变量：height和weight，以及public void speakHello()、public void averageHeight()、public void averageWeight()方法。

好的，下面是一个符合要求的Java应用程序的实现。其中，`People`类是父类，`ChinaPeople`、`AmericanPeople`和`BeijingPeople`类都是子类，继承了`People`类的属性和方法。

People类的实现：

public class People {
    protected double height;
    protected double weight;

    public void speakHello() {
        System.out.println("Hello, I am a people.");
    }

    public void averageHeight() {
        System.out.println("The average height of people is 1.75 meters.");
    }

    public void averageWeight() {
        System.out.println("The average weight of people is 70 kilograms.");
    }
}

ChinaPeople类的实现：

public class ChinaPeople extends People {
    public ChinaPeople(double height, double weight) {
        this.height = height;
        this.weight = weight;
    }

    public void speakHello() {
        System.out.println("你好，我是中国人。");
    }

    public void averageHeight() {
        System.out.println("中国人的平均身高为：1.68米。");
    }

    public void averageWeight() {
        System.out.println("中国人的平均体重为：65公斤。");
    }
}

AmericanPeople类的实现：

public class AmericanPeople extends People {
    public AmericanPeople(double height, double weight) {
        this.height = height;
        this.weight = weight;
    }

    public void speakHello() {
        System.out.println("Hello, I am an American.");
    }

    public void averageHeight() {
        System.out.println("The average height of American people is 1.78 meters.");
    }

    public void averageWeight() {
        System.out.println("The average weight of American people is 80 kilograms.");
    }
}

BeijingPeople类的实现：

public class BeijingPeople extends ChinaPeople {
    public BeijingPeople(double height, double weight) {
        super(height, weight);
    }

    public void speakHello() {
        System.out.println("你好，我是北京人。");
    }

    public void averageHeight() {
        System.out.println("北京人的平均身高为：1.72米。");
    }

    public void averageWeight() {
        System.out.println("北京人的平均体重为：70公斤。");
    }
}

Main类的实现：

public class Main {
    public static void main(String[] args) {
        People people = new People();
        people.speakHello();
        people.averageHeight();
        people.averageWeight();

        ChinaPeople chinaPeople = new ChinaPeople(1.70, 60);
        chinaPeople.speakHello();
        chinaPeople.averageHeight();
        chinaPeople.averageWeight();

        AmericanPeople americanPeople = new AmericanPeople(1.80, 70);
        americanPeople.speakHello();
        americanPeople.averageHeight();
        americanPeople.averageWeight();

        BeijingPeople beijingPeople = new BeijingPeople(1.75, 65);
        beijingPeople.speakHello();
        beijingPeople.averageHeight();
        beijingPeople.averageWeight();
    }
}

在这个例子中，我们定义了四个类，分别是`People`、`ChinaPeople`、`AmericanPeople`和`BeijingPeople`。`People`类是父类，包含了共有的属性和方法。`ChinaPeople`、`AmericanPeople`和`BeijingPeople`类都继承了`People`类，并重写了其中的方法。

在`Main`类中，我们创建了四个对象，分别是`People`、`ChinaPeople`、`AmericanPeople`和`BeijingPeople`，并调用它们的方法。需要注意的是，由于`ChinaPeople`和`AmericanPeople`都是`People`类的子类，因此它们也可以直接调用`People`类中的方法。而`BeijingPeople`类继承了`ChinaPeople`类，因此它可以调用`ChinaPeople`类和`People`类中的方法。