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Editorial Team
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Asked: 2026-05-31T14:56:12+00:00

I have created an applet which has a necessity to execute the following code:

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I have created an applet which has a necessity to execute the following code:

Code

public class Example extends JApplet {
private ServerSocket ss ;
private Socket socket;
private boolean closed;

@Override
public void init(){
    try {
        new Example().initialize();
    } catch (IOException ex) {
        Logger.getLogger(Example.class.getName()).log(Level.SEVERE, null,ex);
    }
}
public void closed(){
    System.out.println("Inside close");
    this.closed=true;
  }
public void initialize() throws IOException{
    ss =new ServerSocket(5002);
    while(!closed){
    System.out.println("Waiting to accept request");
    socket = ss.accept();
    System.out.println("Request accepted");
    } 
}}

HTML

Fragment of HTML file to execute applet:

<script type="text/javascript" >  
 function closeCall(){  
 document.app.closed();  
 }  
 </script>  
   <body>  
<applet id="app" code="example.Example" archive="Example.jar" height="300" width="300">    
   </applet>  
   <input type="button" value="go" onClick="closeCall()" />

Problem: On clicking Go my browser stops responding and there is no error in javascript code as well. Is there any way to call the document.app.closed(); method?

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1 Answer

  1. Editorial Team

    It was only after turning that code into an SSCCE1 that the many problems became clear:

    • This code failed for me without any sign of JS. That indicates to me that this has nothing to do with JS!
    • The instance of Example on which initialize() was called was not the same as that which was the applet! It did not matter if the UI ever detected the JS, it would not have stopped the running instance.
    • The accept() was blocking the EDT.
    • Setting closed to true was not about to have an effect until after the next client connected and the code looped around to check the value of the closed attribute again. I achieved it by calling ss.close() (which makes the closed attribute redundant BTW – but I left it in).

    BTW

    1. Please consider posting an SSCCE in future.

    Code

    Try this version:

    // <applet code='Example' width=400 height=100></applet>
import java.awt.event.*;
import javax.swing.*;
import java.net.*;
import java.io.*;
import java.util.logging.*;

public class Example extends JApplet {
    private ServerSocket ss ;
    private Socket socket;
    private boolean closed;

    @Override
    public void init(){
        JButton stop = new JButton("Stop!");
        stop.addActionListener( new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                closed();
            }
        });
        add( stop );
        validate();

        Runnable r = new Runnable() {
            public void run() {
                try {
                    initialize();
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        };
        Thread t = new Thread(r);
        t.start();
    }

    public void closed() {
        System.out.println("Inside close");
        closed=true;
        try {
            ss.close();
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    public void initialize() throws IOException {
        ss =new ServerSocket(5002);
        while(!closed){
            System.out.println("Waiting to accept request");
            socket = ss.accept();
            System.out.println("Request accepted");
        }
    }
}

    Run

    I have added a button to this version so that you can check it works as expected without JavaScript (which you should have checked with your own code before tossing JS into the mix). The single line comment at the top of the source is used by AppletVewer to put the code on-screen. Use it like this:

    prompt> appletviewer Example.java

    Typical Output

    Waiting to accept request
Inside close
java.net.SocketException: socket closed
    at java.net.PlainSocketImpl.socketAccept(Native Method)
    at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:408)
    at java.net.ServerSocket.implAccept(ServerSocket.java:462)
    at java.net.ServerSocket.accept(ServerSocket.java:430)
    at Example.initialize(Example.java:51)
    at Example$2.run(Example.java:27)
    at java.lang.Thread.run(Thread.java:662)

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