pump.java

程序练习中包括书中实例程序代码和练习中要用到的代码,是压缩文件

package examples.observe;

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

/** Class to demonstrate the use of the Observer
  * interface and the Observable class
  */
public class Pump {
   /** Method for creating a Pump, a Valve, and
     * a Buzzer object and connecting the Valve
     * and Buzzer objects together
     * @param args not used
     */
   public static void main( String[] args ) {
      Pump p = new Pump();
      Valve v = p.new Valve();
      Buzzer b = p.new Buzzer();
      v.addObserver( b );

      v.setPressure( 150 );
      v.setPressure( 200 );
      v.setPressure( 75 );
   }

   /** A class representing a valve in a pump
     * that can be observed by other objects
     */
   private class Valve extends Observable {

      private int pressure;

      /** Method used to set the pressure at
        * the valve.  It notifies its
        * observers of the change
        * @param p Updated pressure value
        */
      public void setPressure( int p ) {
         pressure = p;
         setChanged();
         notifyObservers();
      }

      public int getPressure() {
         return pressure;
      }
   }

   /** Class representing the warning buzzer on a
     * pump.  The buzzer sounds when the pressure
     * of the valve it is observing exceeds the
     * threshold, and goes silent when the pressure
     * drops back below the threshold.
     */
   private class Buzzer implements Observer {

      private int threshold = 100;
      private boolean buzzerOn;

      /** This method is called whenever the valve
        * being observed changes
        * @param o the object under observation
        * @param arg optional argument, not used
        */
      public void update( Observable o, Object arg ) {
          Valve v = (Valve) o;
          if ( v.getPressure() > threshold
               && buzzerOn == false ) {
             buzzerOn = true;
             System.out.println( "Buzzer on" );
          } else if ( v.getPressure() < threshold
                      && buzzerOn == true ) {
             buzzerOn = false;
             System.out.println( "Buzzer off" );
          }
      }
   }
}