Listening for data, is while(true) the correct solution? Java

Question

I have faced a problem i hope someone here can help me with. Right now, I have used way too many while(true) loops in my program, so it runs a little slow.

I'm not sure if i am doing something wrong with my code, or if this is the only solution.

Have a class which receive data (doubles) from another class. Want to start a while loop which only should run when the data is not 0. Some code i have here:

while (true) {
        while (kWh != 0) {
            try {
                queue.put(kWh);
            } catch (InterruptedException e) {                  
                System.out.println("Could not put data into queue");
            }
            kWh = 0;
        }   
    }





@Override
public void SendPower(double power_data) throws RemoteException {
    ReceivePowerData.kWh = power_data;              
}

As you can see, when the SendPower method runs, the kWh variable gets updated. When this variable is not 0, i want the while loop to run and insert the value to the queue. My problem is that i am using while(true) so it keeps running that loop, even when no data are received, and that is a waste.

What can i else do? any idea?

Update

I have tried to use the wait(); method, and that seem to work, it waits.. but i don't know how i should implement the notify(); method which should start it again.

code:

synchronized (this) {
        System.out.println("Wait for response from sensor");
        try {
            wait();
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
        System.out.println("Continue");

        while (kWh != 0) {
            try {
                queue.put(kWh);
            } catch (InterruptedException e) {                  
                System.out.println("Could not put data into queue");
            }
            kWh = 0;
        }   

    }

Then i tried to code it in the method, but i really think this is wrong..

@Override
public void SendPower(double power_data) throws RemoteException {
    ReceivePowerData.kWh = power_data;  

    synchronized (this) {
        notify();   
    }

}

So when the SendPower method are called from another program, it should run, and then it should start, but this does not work.. am i close?

Answer 1

You can use the observer pattern. Java has standard interfaces to implement it.

There are loads of tutorials on this pattern in Java

http://en.wikipedia.org/wiki/Observer_pattern http://www.tutorialspoint.com/design_pattern/observer_pattern.htm

This is a very simplistic example.

import java.util.Observable;
import java.util.Observer;
import java.util.Random;

public class ObserverPattern {
    private static class PowerObserverable extends Observable implements Runnable {

        public void run() {
            Random random = new Random();
            for (int x = 0; x < 10; x++) {
                double kwh = random.nextDouble() * 4;
                setChanged();
                notifyObservers(kwh);
            }
        }
    }

    // Make sure this class is thread safe
    private static class PowerObserver implements Observer {
        @Override
        public void update(Observable o, Object kwh) {
            System.out.println(kwh);
        }
    }

    public static void main(String[] args) {
        PowerObserverable observerable = new PowerObserverable();
        observerable.addObserver(new PowerObserver());

        new Thread(observerable).start();
    }
}