Question

I don’t know how to implement an action listener from separate ActionListener class. I have divided application in several classes. Main class calls the Frame class to create GUI with all the buttons. Now when the button is pressed i need to send some data to ActionListener method for it to do the work. If I add ActionListener in Frame class than I cant send needed data, if I add ActionListener in main() method, after calling Frame class it feels clumsy.
Here is the code:
public class Main {

public static Client klijent;

public static void main(String[] args) {

    FrameBuilder frame= new FrameBuilder();
    frame.frameBuild();
    frame.send.addActionListener(new SendBttnListener(ClientBuilder(klijent,frame.txt.getText())));

    try {
        frame.statLabel.setText(InetAddress.getLocalHost().getHostAddress());
    } catch (UnknownHostException e) {
        e.printStackTrace();
    }

    Udp udp;
    // klijent = null;

    while(true){
        klijent=new Client();
        udp=new Udp();

        klijent=udp.packageIN();
        if(klijent!=null){
            frame.statLabel.setText("");
            String str=new String(klijent.getBajt(),0,klijent.bajt.length);
            str=str.trim();
            frame.statLabel.setText(str+"@...@"+klijent.clientAddress.toString()+":"+klijent.clientPort+"-->Duljina:"+klijent.bajt.length);
        }
    }
}

public static Client ClientBuilder(Client klijent2, String str){

    klijent.setBajt(str.getBytes());

    return klijent2;
}

As u can see Client object can change a lot (UDP server) and will be cleared when waiting for next package. Later I think of implementing some list of Clients and adding Action listener in Frame class seems stupid. Did i go wrong when I created separet class for building GUI? Any advice?

Thanks in advance….

Answer 1

The method by which you send should be wrapped up in it’s own implementation. This could be a singlton implementation or passed as reference to a wrapping action listener.

The buttons action listener should only be manged from within the context of the button, it should not be accessible from out side the buttons context (ie I don’t believe you should be able to do this frame.send.addActionListener(...)) as callers shouldn’t care how a send request is achieved, just that it is…

I’d have a class or interface that you could pass to your frame that provided it with the means to “send” a message.

public interface Sender {
    public void sendMessage(String message); // Or what ever parameter you want...
}

I’d pass a reference of the implementation to your frame…

Sender sender = new ImplementationOfSender();
frame.setSender(sender); // It could also be passed to the constructor

In the frame, I would attach my action listener to the button and when triggered, I would access the sender and send the message…

send.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent evt) {
        Sender sender = getSender();
        if (sender != null) {
            sender.sendMessage(...);
        }
    }
});

Now having said all that…your program is going to blow up in your face real quick…

This is going to stop your program in it’s tracks, making the UI look like it’s hung.

while(true){
    klijent=new Client();
    udp=new Udp();

    klijent=udp.packageIN();
    if(klijent!=null){
        frame.statLabel.setText("");
        String str=new String(klijent.getBajt(),0,klijent.bajt.length);
        str=str.trim();
        frame.statLabel.setText(str+"@...@"+klijent.clientAddress.toString()+":"+klijent.clientPort+"-->Duljina:"+klijent.bajt.length);
    }
}

All interactions with the UI MUST be done from within the context of the Event Dispatching Thread (AKA EDT). Any blocking actions, such as your loop, should NEVER be executed from within the context of the EDT

I would have read of Concurrency in Swing.

The only reason that you program probably has exploded yet is the fact that when you launch it, you’ve not synced the creation of your UI to the EDT.

You might like to have a read of Swing Single Threading Rule