//file: Multiplier.javapackage magicbeans;import java.beans.*;public class Multiplier implements java.io.Serializable {  private double a, b, c;  synchronized public void setA( double val ) {    a = val;    multiply(  );  }  synchronized public double getA(  ) {    return a;  }  synchronized public void setB( double val ) {    b = val;    multiply(  );  }  synchronized public double getB(  ) {    return b;  }  synchronized public double getC(  ) {    return c;  }  private void multiply(  ) {    double oldC = c;    c = a * b;    propChanges.firePropertyChange(      "c", new Double(oldC), new Double(c));  }  private PropertyChangeSupport propChanges =      new PropertyChangeSupport(this);  public void  addPropertyChangeListener(PropertyChangeListener listener) {    propChanges.addPropertyChangeListener(listener);  }  public void  removePropertyChangeListener(PropertyChangeListener listener) {    propChanges.removePropertyChangeListener(listener);  }}