带有包含
class MyApplication观察到另一个类，并且自身也被观察到。问题是"update"方法对布尔值replyOne和replyTwo的更新对"run"方法不可见。我希望运行MyApplication类的多个副本，因此不希望使用static关键字。有没有办法让run方法在不使用static关键字修改布尔值的情况下查看布尔值的更改？
观察到的和MyApplication类由另一个类启动，如下所示：
final ServerOne firstServer = new ServerOne();
MyApplication appOne = new MyApplication();
// subscribe the observers to the observed - eberybody watches each other
firstServer.addObserver(appOne);
appOne.addObserver(firstServer);
// start the threads
Thread firstServerThread = new Thread(firstServer,"firstServer");
firstServerThread.start();
Thread thread3 = new Thread(appOne, "appOne");
thread3.start();
MyApplication类的代码如下：
public class MyApplication extends Observable implements Observer, Runnable {
private String resp, response;
private long timeTaken;
private boolean replyOne,replyTwo;
@Override
public void update(Observable observable, Object arg) {
timeTaken = (System.nanoTime() - ((Long) arg).longValue()) / 1000;
if (observable instanceof ServerOne) {
//process ObservableCLass1 update here
System.out.println("App Thread " + Thread.currentThread().getName() + " received update from serverOne in " + timeTaken + " microSecs");
this.replyOne = true;
} else if (observable instanceof ServerTwo) {
System.out.println("App Thread " + Thread.currentThread().getName() + " received update from serverTwo in " + timeTaken + " microSecs");
this.replyTwo = true;
}
timeTaken = ((Long) arg).longValue();
setChanged();
notifyObservers(timeTaken);
clearChanged();
}
public void run() {
this.replyOne = false;
this.replyTwo = false;
while (!this.replyOne || !this.replyTwo) {
// wait until the observer has set both the reply flags
if (this.replyOne) {
System.out.println("Reply one True ");
setChanged();
notifyObservers(new String("app Calling after update from serverOne "));
this.replyOne = false;
}
if (this.replyTwo) {
System.out.println("Reply two True ");
setChanged();
notifyObservers(new String("app Calling after update from serverTwo "));
this.replyTwo = false;
}
}
}
}
存在多个问题。首先，看看你的run方法：
this.replyOne = false;
this.replyTwo = false;
while (!this.replyOne && this.replyTwo) {
首先将两个变量都设置为false，然后如果replyTwo是true，则进入循环，这是不太可能发生的。很可能，你的意思是：while (!this.replyOne && !this.replyTwo)。
但整个结构看起来很可疑。很明显，这里缺少的等待代码应该在一个循环中等待它至少一个标志变成true，但为什么通知也在循环中？run方法应在何种情况下再次等待，何时退出？
也许你过于简单化了。预期的代码可能是这样的：
this.replyOne = false;
this.replyTwo = false;
while(!endCondition) {
while (!this.replyOne && !this.replyTwo) {
// wait until the observer has set both the reply flags
}
if (this.replyOne) {
System.out.println("Reply one True ");
setChanged();
notifyObservers(new String("app Calling after update from serverOne "));
this.replyOne = false;
}
if (this.replyTwo) {
System.out.println("Reply two True ");
setChanged();
notifyObservers(new String("app Calling after update from serverTwo "));
this.replyTwo = false;
}
}
我假设您将一个正确的线程安全构造放在注释中"等待观察者设置了两个回复标志"的位置。否则就没有内存可见性的保证，换句话说，即使另一个线程修改了其中一个变量，这个循环也可能无限运行。
replyOne和replyTwo的额外事件类对象的notifyObservers将是经典方式。
public class ReplyEvent {
public boolean replyOne;
...
}
ReplyEvent evt = new ReplyEvent();
evt.message = "...";
evt.replyOne = replyOne;
...
notifyObservers(evt);