我怎样才能找到观察的平均值?

我真的很难处理这个类,它生成一个随机数并更新观察者的类。我怎样才能找到生成的所有这些随机数的平均值?(observations\u avg)并将其传递给观察员

A类

public abstract class A implements Observer {
     public abstract String disp();
     public abstract void update(Observable subject, Object o);
}

B类

public class B extends A {

    public double limit;
    public B(double limit) {
         this.limit = limit;
    }
    public void update(Observable o, Object arg) {
         if (observations_avg >= limit) {
              System.out.println(disp());
         }
    }
    public String disp() {  
    // observations_avg = sum of all observation, and divide it by the    quantity of them
         String d = "WARNING avg exceeded limit: " + observations_avg;
         return d;
    }
}

C类

public class C extends A {

    Avg avg = new Avg(10);
    public void update(Observable subject, Object o) {
        System.out.println(disp());
    }
    public String disp() { 
        String d = "avg is " observations_avg+ ; // i want to display the average of all the random numbers
        return d;
    }
}

生成随机数并更新观察员类平均值

public class Avg extends Observable {

    private int seed;
    Random random = new Random();
    public Avg(int seed) {
        this.seed = seed;
        random.setSeed(this.seed);
    }
    public double getRandom() {
        double r = random.nextDouble()*10;
        return r;
    }
    public void read() {
        setChanged();
        notifyObservers();
    }
}

主要

public class Main {
    public static void main(String[] args) {

        Avg avg = new Avg(10);
        // create observers and add them
        B B_obj = new B(8);
        C C_obj = new C();
        avg.addObserver(B_obj);
        avg.addObserver(C_obj);

        try {
            while (true) {
                avg.read();
                Thread.sleep(1000);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }   
    }
}

提前谢谢你。