java - Observer - 围绕电子邮件接收逻辑的可观察模型

Question

我编写了一个电子邮件接收逻辑(类名:Mail_Receive_Logic)。此类将我所有未读的电子邮件下载到 messages 数组中。

我还有类 EmailStatPrinter 和 EmailStatRecorder 类。 EmailStatPrinter 有一个 writeToConsole 方法，可以将数组打印到屏幕上。 EmailStatRecorder 有一个 writeToFile 方法，可将数组写入文本文件中。

我想以观察者可观察的方式实现这个逻辑。

public class Mail_Receive_Logic extends Observable{ 
public class EmailStatPrinter implements Observer{
public class EmailStatRecorder implements Observer{

我的主要方法如下所示

public static void main(String[] args) throws ClassNotFoundException {

    // observable
    Mail_Receive_Logic receiveMail = new Mail_Receive_Logic(usernameReceiving, passwordReceiving, fileReceivePath);

    // observer
    EmailStatPrinter writeToConsole = new EmailStatPrinter();
    EmailStatRecorder writeToFile = new EmailStatRecorder();

    receiveMail.addObserver(writeToConsole);
    receiveMail.addObserver(writeToFile);

    Thread receive = new Thread (new Runnable() {
        public void run() { 
            try {
                while (true) {
                    receiveMail.receive();  
                }
            } catch (InterruptedException e) {}
        }
    }); 

    receive.start();

我应该如何编写每个观察者类的更新方法，以便它们接收消息数组并将其打印在控制台和文本文件上。即我想知道在以下代码段中为每个观察者类编写什么。

@Override
    public void update(Observable o, Object arg) {
        // TODO Auto-generated method stub

    }

还请解释一下为什么有 2 个变量 Observable o 和 Object arg？

Answer 1

您必须调用Observable.notifyObservers()并提供arg。它可以是任何你喜欢的东西。就你而言，我认为你会想要这样的东西:

try {
    while (true) {
        receiveMail.receive();
        receiveMail.notifyObservers(messages);
    }
}
catch (InterruptedException e) {
}

然后在您的观察者中您将收到以下消息:

@Override
public void update(Observable o, Object arg) {
    // The first arg is the thing you were observing (receiveMail in this case)
    // The second arg is the messages that was passed by the receiveMail instance
}