java 内部类与控制框架

应用程序控制框架(application framework)就是设计解决某类特殊问题的一个类,或一组类,要运用某个应用程序框架,通常是继承一个类或多个类,并覆盖这些方法.在覆盖的方法中编写代码定制应用程序框架提供的解决方案,以解决你的问题

控制框架是一类特殊应用程序框架,它用来解决响应事件的需求,主要用来响应事件的系统被称为事件驱动系统,(最常见的是GUI)

应用框架设计中,设计的关键是"变化的事物和不变的事物相互分离"

//: innerclasses/controller/Event.java
// The common methods for any control event.
package object;

public abstract class Event {//因为其默认的行为是基于时间去执行控制的,所以使用抽象类代替实际的接口
  private long eventTime;
  protected final long delayTime;
  public Event(long delayTime) {
    this.delayTime = delayTime;
    start();
  }
  public void start() { // Allows restarting//当运行Event并调用start()时,构造器就会捕获时间
    eventTime = System.nanoTime() + delayTime;//当前时间加上延迟时间,start()是一个独立方法,而没有包含在构造器中
  }                                           //这样就可以在事件运行以后重新启动计时器
  public boolean ready() {
    return System.nanoTime() >= eventTime;
  }
  public abstract void action();//对于控制行为,控制框架并不包含具体的信息,那些算的action()部分通过继承action()来来提供
} ///:~

下面的是一个用来管理并触发事件的实际控制框架,

//: innerclasses/controller/Controller.java
// The reusable framework for control systems.
package object;
import java.util.*;

public class Controller {
  // A class from java.util to hold Event objects:
    //List是一个容器,list<Event>(读作Event的列表>
    //add()添加Object到LIst的尾端, size()得到List中的元素个数
    //foreach语法用来连续获取List中的Event
    //remove()方法用来从list列表移除指定的Event
  private List<Event> eventList = new ArrayList<Event>();
  public void addEvent(Event c) { eventList.add(c); }
  public void run() {  //该方法遍历eventlist,寻找就绪的ready(),并调用相应的方法
    while(eventList.size() > 0)
      // Make a copy so you're not modifying the list
      // while you're selecting the elements in it:
      for(Event e : new ArrayList<Event>(eventList))
        if(e.ready()) {
          System.out.println(e);
          e.action();
          eventList.remove(e);
        }
  }
} ///:~

内部类允许:

1)控制框架的完整是由单个的类创建的,从而使得实现的细节被封装了起来,内部类用来表示解决问题所必需的各种不同的action()

2)内部类能够很容易地访问外围类的任意成员,所以可以避免这种实现变得笨拙,

下面是此框架的一个特定实现,控制温度的运作:控制灯光,水,温度调节器的开关,以及响铃和重新启动系统,每个行为都是完全不同的,控制框架的设计使得分离这些不同的代码变得非常容易,使用内部类,可以在单一的类里面产生对同一个基类Event的多种导出版本,对于温度系统的每一种行为,都继承一个新的Event内部类,并在要实现的action()中编写控制代码

//: innerclasses/GreenhouseControls.java
// This produces a specific application of the
// control system, all in a single class. Inner
// classes allow you to encapsulate different
// functionality for each type of event.
package object;

public class GreenhouseControls extends Controller {
  private boolean light = false;
  public class LightOn extends Event {
    public LightOn(long delayTime) { super(delayTime); }
    public void action() {
      // Put hardware control code here to
      // physically turn on the light.
      light = true;
    }
    public String toString() { return "Light is on"; }
  }
  public class LightOff extends Event {
    public LightOff(long delayTime) { super(delayTime); }
    public void action() {
      // Put hardware control code here to
      // physically turn off the light.
      light = false;
    }
    public String toString() { return "Light is off"; }
  }
  private boolean water = false;
  public class WaterOn extends Event {
    public WaterOn(long delayTime) { super(delayTime); }
    public void action() {
      // Put hardware control code here.
      water = true;
    }
    public String toString() {
      return "Greenhouse water is on";
    }
  }
  public class WaterOff extends Event {
    public WaterOff(long delayTime) { super(delayTime); }
    public void action() {
      // Put hardware control code here.
      water = false;
    }
    public String toString() {
      return "Greenhouse water is off";
    }
  }
  private String thermostat = "Day";
  public class ThermostatNight extends Event {
    public ThermostatNight(long delayTime) {
      super(delayTime);
    }
    public void action() {
      // Put hardware control code here.
      thermostat = "Night";
    }
    public String toString() {
      return "Thermostat on night setting";
    }
  }
  public class ThermostatDay extends Event {
    public ThermostatDay(long delayTime) {
      super(delayTime);
    }
    public void action() {
      // Put hardware control code here.
      thermostat = "Day";
    }
    public String toString() {
      return "Thermostat on day setting";
    }
  }
  // An example of an action() that inserts a
  // new one of itself into the event list:
  public class Bell extends Event {
    public Bell(long delayTime) { super(delayTime); }
    public void action() {
      addEvent(new Bell(delayTime));//Bell控制响铃然后再事件列表中增加一个Bell对象,于是过一会二它可以再次响铃
    }
    public String toString() { return "Bing!"; }
  }
  public class Restart extends Event {//Restart()可以控制系统有规律的重启
    private Event[] eventList;
    public Restart(long delayTime, Event[] eventList) {
      super(delayTime);
      this.eventList = eventList;
      for(Event e : eventList)
        addEvent(e);
    }
    public void action() {
      for(Event e : eventList) {
        e.start(); // Rerun each event
        addEvent(e);
      }
      start(); // Rerun this Event
      addEvent(this);
    }
    public String toString() {
      return "Restarting system";
    }
  }
  public static class Terminate extends Event {
    public Terminate(long delayTime) { super(delayTime); }
    public void action() { System.exit(0); }
    public String toString() { return "Terminating";  }
  }
} ///:~

下面的类通过创建一个GreenhouseControls对象,并添加各种不同的Event对象来配置该系统,这是命令设计模式的一个例子再eventlist中的每一个被封装成对象的请求

//: innerclasses/GreenhouseController.java
// Configure and execute the greenhouse system.
// {Args: 5000}
package object;
public class GreenhouseController {
  public static void main(String[] args) {
    GreenhouseControls gc = new GreenhouseControls();
    // Instead of hard-wiring, you could parse
    // configuration information from a text file here:
    gc.addEvent(gc.new Bell(900));
    Event[] eventList = {
      gc.new ThermostatNight(0),
      gc.new LightOn(200),
      gc.new LightOff(400),
      gc.new WaterOn(600),
      gc.new WaterOff(800),
      gc.new ThermostatDay(1400)
    };
    gc.addEvent(gc.new Restart(2000, eventList));
    if(args.length == 1)
      gc.addEvent(
        new GreenhouseControls.Terminate(
          new Integer(args[0])));

    gc.run();
  }
} /* Output:
Bing!
Thermostat on night setting
Light is on
Light is off
Greenhouse water is on
Greenhouse water is off
Thermostat on day setting
Restarting system
Terminating
*///:~