Btukfyl

I have a class which implement an interface from third part library and one of methods is passing object of class called Velocity.

How I can listen to specific variable value changes in this object?

Here is the code for better understanding.

This is interface from the third part library :

public interface MotionListener {

    void onObjectMoved(Velocity velocity);

    void onObjectStopped();

}

and the Velocity class is packed in the library and it is very simple.
The class has 3 attributes.
I implemented this interface in my class as follows:

public class MyCar implements MotionListener {



    @Override

    public void onObjectMoved(Velocity velocity) {

        System.out.println("Distance" + velocity.getDistance());

        System.out.println("Speed" + velocity.getSpeed());

        System.out.println("widnowIsOpened" + velocity.widnowIsOpened());



         /* 

I need here to set up a listener for the boolean value widnowIsOpened 

because this boolean may be change later and this method will not be invoked again 

, it is just invoked once but 

value of windowIsOpened may change by the library 

*/

    }



    @Override

    public void onObjectStopped() {



    }

    // other methods ...

}

What I need is to listen to the boolean value changes to react to the changes in my code. I did a lot of searching on this topic, but all possible solutions that i found if I have access to Velocity class so I can set listener inside the Velocity class,
but in my case I have only the passed object.
So the only thing I can do is to check if the
widnowIsOpened is true or false, but not for change.

Any help?

You can write your custom listener class with some method in that class. Call that method of listener class inside onObjectMoved() method based on the boolean value.
If you want to send update to multiple listeners, then write a interface for listener and writes its implementations.
If you want I can share some piece of code with you.

Here you go:

public class MyCar implements MotionListener {



private VelocityListener listener;



// added constructor

public MyCar(VelocityListener listener) {

    this.listener = listener;

}



@Override

public void onObjectMoved(Velocity velocity) {

    System.out.println("Distance" + velocity.getDistance());

    System.out.println("Speed" + velocity.getSpeed());

    System.out.println("isMoving" + velocity.isMoving());

    // added handling

    listener.doSomething(velocity);



    // I need here to set up a listener for the boolean value isMoving

}



@Override

public void onObjectStopped() {



}



public static void main(String args) {

    MyCar car = new MyCar(new VelocityListenerImpl());

    //if you are using java 8 then you can use functional interface like below

    //MyCar otherCar = new MyCar(()->{System.out.println("velocity changed....");});

}

}

Listener and its implementation

public interface VelocityListener {

public void doSomething(Velocity velocity);}



public class VelocityListenerImpl implements VelocityListener {

public void doSomething(Velocity velocity) {

    while (true) {

        if (velocity.isMoving()) {

            System.out.println("velocity changed....");

        }

    }

}}

is actually the oposite, the car need the interface but no need to implement it

public interface MotionListener {

    void onObjectMoved(Velocity velocity);

    void onObjectStopped();

}



public class MyCar {

    private MotionListener myMotionListener;

    private void setMotionListener(MotionListener someMotionListener){

        myMotionListener= someMotionListener;

    }



    public void doSomething(){

        if(myMotionListener != null){

            myMotionListener.onObjectMoved(myVelocity);

        }

    }   

    public void notifiyamStop(){

        if(myMotionListener != null){

            myMotionListener.onObjectStopped();

        }

    }   



// other methods ...



}



public class MyPolice implements MotionListener {



    @Override

    public void onObjectMoved(Velocity velocity) {

        System.out.println("Distance" + velocity.getDistance());

        System.out.println("Speed" + velocity.getSpeed());

        System.out.println("isMoving" + velocity.isMoving());



         // i need here to setup a listener for the boolean value isMoving 

    }



    @Override

    public void onObjectStopped() {



    }

// other methods ...

}

Apparently, MotionListener is the listener. You need to implement it. Each time MyCar moves, the OnObjectMoved() and OnObjectStopped() methods are called. In those methods, do whatever needs to happen when the car moves or stops, such as recalculating the position.

As far as listeners, the listener will be called by the external entity each time the velocity changes. So, your method simply needs to look at the value and do something with it. I'm guessing Velocity has getters for speed and direction.