import java.io.*;
import java.beans.*;

public class Multiplier implements Serializable {
  private double a, b, result;

  synchronized public void setA(double newA) {
     a = newA;
     multiply();
  } 

  synchronized public double getA() {
     return a;
  } 

  synchronized public void setB(double newB) {
     b = newB;
     multiply();
  }

  synchronized public double getB() {
     return b;
  }

  synchronized public void setResult(double d) {
     multiply();
  }

  synchronized public double getResult() {
     return result;
  }

  private void multiply(){
     double oldRes = result;
     result = a * b;
     //registrera det nya resultatet
     propChanges.firePropertyChange("result", new Double(oldRes), new Double(result));
  } 

  //skapa stöd för att avlyssna egenskapsförändring
  private PropertyChangeSupport propChanges = new PropertyChangeSupport(this);

  //metod som lägger till lyssnare
  public void addPropertyChangeListener(PropertyChangeListener listener) {
     propChanges.addPropertyChangeListener(listener);
  } 

  //metod som tar bort lyssnare
  public void removePropertyChangeListener(PropertyChangeListener listener) {
     propChanges.removePropertyChangeListener(listener);
  }
     
}