Question

Sorry for the confusing title, I’m not sure how to describe it in minimal words but basically what I’m trying to do is return a LinkedList from a method. But I wanna put the actual content inside the method inside a Thread, and then return the data when the thread is done. Here is the code I am using:

public static LinkedList<Result> get(final String prefix){
    final LinkedList<Result> results = new LinkedList<Result>();
    if(thread != null){
        thread.stop();
        thread = null;
    }
    thread = new Thread(
            new Runnable(){
                public void run(){
                    try{
                        URL url = new URL(String.format(URL_INFO, prefix));
                        URLConnection connection = url.openConnection();
                        connection.setReadTimeout(Timeout.TIMEOUT);
                        connection.setConnectTimeout(Timeout.TIMEOUT);
                        InputStream is = connection.getInputStream();
                        Scanner reader = new Scanner(is);
                        while(reader.hasNextLine()){
                            String line = reader.nextLine();
                            if(line != null){
                                if(line.contains(String.format(WORDS_INFO, prefix))){
                                    String[] s = line.split(String.format(PREFIX_INFO, prefix));
                                    String[] s2 = s[1].split("\">");
                                    if(s2.length > 0){
                                        for(int i = 1; i < s2.length; i++){
                                            String l = s2[i];
                                            String[] split = l.split(FINAL_SPLIT);
                                            results.add(new Result(prefix, split[0].trim()));
                                        }
                                    }
                                    break;
                                }
                            }
                        }
                        reader.close();
                    }catch(Exception e){
                        e.printStackTrace();
                    }
                }
            }
    );
    thread.start();
    return results;
}

The thread is statically defined inside the variables section. And basically the problem here is that it returns an empty LinkedList because it’s not waiting for the Thread to be finished. How can I wait until the Thread is finished before returning the LinkedList? Any help would be greatly appreciated. Thanks.

NOTE: The issue is not anything to do with reading the URL, the problem is is that it’s returning an empty LinkedList because the Thread has not finished yet and I want to know how to wait until the Thread is done before it returns something.

Answer 1

You need to wait till the thread completes execution. Look up the documentation on Thread.join.

This is just one way to do what you are trying. There are many others, such as ExecutorService