Java 事件链

Java中的事件机制的参与者有3种角色：

1. event object：就是事件产生时具体的“事件”，用于listener的相应的方法之中，作为参数，一般存在于listerner的方法之中
2. event source：具体的接受事件的实体，比如说，你点击一个button，那么button就是eventsource，这样你必须使button对某些事件进行响应，你就需要注册特定的listener，比如说MouseEvent之中的MouseClicked方法，这时它就必须有了add方法
3. event listener：具体的进行监听的事件类，当有其对应的event object产生的时候，它就调用相应的方法，进行处理。在windows程序设计里边这种响应使用callback机制来实现的

import org.junit.jupiter.api.Test;

public class MonitorTest {

    @Test
    public void monitoringTest() throws Exception {
        MonitorManager manager=new MonitorManager();
        manager.addListener(new CarListener());
        manager.addListener(new BicycleListener());
        manager.addListener(new PersonListener());
        manager.straight();
        System.out.println("=======================");
        manager.turnLeft();
    }
}

import java.util.EventObject;

public class MonitorEvent extends EventObject {

    /**
     * 1 直行绿灯
     * 2 左拐绿灯
     */
    private Integer heartRateValue;

    public MonitorEvent(Object source, Integer heartRateValue) {
        super(source);
        this.heartRateValue = heartRateValue;
    }

    public Integer getHeartRateValue() {
        return heartRateValue;
    }

    public void setHeartRateValue(Integer heartRateValue) {
        this.heartRateValue = heartRateValue;
    }
}

import java.util.EventListener;

public interface MonitorListener extends EventListener {

    void monitorEvent(MonitorEvent event);

}

import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;

public class MonitorManager {

    private Collection listeners; //存储所有注册进来的事件监听器对象;
    public void addListener(MonitorListener listener) //把一个事件监听器对象注册进来;
    {
        if(this.listeners == null)
        {
            this.listeners = new HashSet();
        }
        this.listeners.add(listener);
    }

    public void removeListener(MonitorListener listener) //移除一个已经注册的事件监听器对象;
    {
        if(this.listeners != null)
        {
            this.listeners.remove(listener);
        }
    }

    /**
     * 直行
     */
    protected void straight()
    {
        if(this.listeners != null)
        {
            MonitorEvent event = new MonitorEvent(this, 1);
            notifyListeners(event);
        }
    }

    /**
     * 左拐
     */
    protected void turnLeft()  //触发开门事件
    {
        if(this.listeners != null)
        {
            MonitorEvent event = new MonitorEvent(this, 2);
            notifyListeners(event);
        }
    }

    private void notifyListeners(MonitorEvent event)
    {
        Iterator inter = this.listeners.iterator();
        while(inter.hasNext())
        {
            MonitorListener listener = (MonitorListener)inter.next();
            listener.monitorEvent(event);
        }
    }
}

===管理类

import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;

public class MonitorManager {

    private Collection listeners; //存储所有注册进来的事件监听器对象;
    public void addListener(MonitorListener listener) //把一个事件监听器对象注册进来;
    {
        if(this.listeners == null)
        {
            this.listeners = new HashSet();
        }
        this.listeners.add(listener);
    }

    public void removeListener(MonitorListener listener) //移除一个已经注册的事件监听器对象;
    {
        if(this.listeners != null)
        {
            this.listeners.remove(listener);
        }
    }

    /**
     * 直行
     */
    protected void straight()
    {
        if(this.listeners != null)
        {
            MonitorEvent event = new MonitorEvent(this, 1);
            notifyListeners(event);
        }
    }

    /**
     * 左拐
     */
    protected void turnLeft()
    {
        if(this.listeners != null)
        {
            MonitorEvent event = new MonitorEvent(this, 2);
            notifyListeners(event);
        }
    }

    /**
     * 通知每一个注册上来的监测，去执行
     * @param event
     */
    private void notifyListeners(MonitorEvent event)
    {
        Iterator inter = this.listeners.iterator();
        while(inter.hasNext())
        {
            MonitorListener listener = (MonitorListener)inter.next();
            listener.monitorEvent(event);
        }
    }
}

===三个具体的类

public class CarListener implements MonitorListener {

    public void monitorEvent(MonitorEvent event) {
        if (event.getHeartRateValue() == 1) {
            System.out.println("直行绿灯 汽车 可直行");
        }
        if (event.getHeartRateValue() == 2) {
            System.out.println("左拐绿灯 汽车 可左拐");
        }
    }
}

public class BicycleListener implements MonitorListener {

    public void monitorEvent(MonitorEvent event) {
        if (event.getHeartRateValue() == 1) {
            System.out.println("直行绿灯 自行车 可直行");
        }
        if (event.getHeartRateValue() == 2) {
            System.out.println("左拐绿灯 自行车 可左拐");
        }
    }
}

public class PersonListener implements MonitorListener {

    public void monitorEvent(MonitorEvent event) {
        if (event.getHeartRateValue() == 1) {
            System.out.println("直行绿灯 人 可直行");
        }
        if (event.getHeartRateValue() == 2) {
            System.out.println("左拐绿灯 人 不可通行");
        }
    }
}