Java在两个类之间无缝传递值

Question

i have rather very basic question. I have one GUI class and another which does some background processing. Normally i have some methods in background class (which consist of multiple threads), which can return the result when called and i can use the result in GUI class.

But now i have this strange problem that the GUI has to display something, which requires background class to call external process and once connected to this process, the connection will remain open, and as such i can not return anything unless the stream is closed. However the process keeps sending data which needs to be displayed on GUI

If i put both in the same class, i can do so; by simple calling eg JLabel.setText(what ever coming from external prcess in infinite while loop). However if it is in a different class, i can not access this JLabel or any such component from another class. If i declare them static, the GUI throws exception, is there anyway i can avoid this, or the only option to write the code together in the same class with the GUI

Answer 1

You have two problems to solve.

First, you need a means to communicate from one class to the other. There are many ways to solve this problem. For example, you could have the worker class publish events subscribed to by the GUI class. Or you could pass to the worker class a reference to the GUI object (possibly as an interface type).

Second, you need to update the GUI only from the event-dispatch thread. You can do this primitively with SwingUtilities.invokeAndWait(Runnable) or SwingUtilities.invokeLater(Runnable) . Or you can use the higher-level framework provided by the SwingWorker class.

Answer 2

You would implement the observer pattern . Something like this:

public interface DataObserver {
   void newDataCame(String someData);
}

public class GUIclass {
    public void method() {
       bgClass.callInBg( new DataObserver() {
           public void newDataCame(String someData) {
               JLabel.setText(someData);
           }
       } );
    }
}

public class BGClass {
    public void callInBg(DataObserver observer) {
        while(true) {
            String data = null;
            // read some data;
            observer.newDataCame(data);
        }
    }
}

This way your background class will notify you GUI class about new data coming from the external process. But you should be careful with GUI updates and GUI thread.

Answer 3

Well you could create a function for setting the text in the GUI class so that you don't need to declare the text field as a public global var. But as for calling from the other class you have two main options. One is to have the other class passed the instance of your GUI class which it can then use to call the method to set the text. The other if you want it to be static is to make your GUI class a singlton class and have a static method that uses it to set the text.

Like this, if your class is called GUI set it up like this:

public class GUI {
     private static GUI singleton = new GUI();
     private GUI(){}
     public GUI getInstance(){
          return singleton;
     }
}

or instead of getInstance and calling the function you could have:

public class GUI {
     private static GUI singleton = new GUI();
     private GUI(){}
     public void setText(){
          //your code
     }

     public static void setTheText(){
          singleton.setText();
     }
}

Be careful with this though, making singleton classes can be dangerous for your design if in the future you ever want to have multiple instances of the class.