How to copy elements of array list from another class to another class

Question

My program encounters an error during execution because the elements of arrlist from NewServer doesn't get copied to MyConnection. What should I do?

MyConnection is responsible for the sending and getting of the message and for the distribution of messages to all the clients.

public class MyConnection extends Thread{
    Socket s;
    BufferedReader in;
    PrintWriter out;
    String reps, msg;
    ArrayList<MyConnection> arrlist;


    MyConnection(Socket s, ArrayList<MyConnection> arrlist){
        this.arrlist = arrlist;
        this.s = s; 

        try{
            this.in= new BufferedReader(new InputStreamReader(s.getInputStream()));
            this.out= new PrintWriter(new OutputStreamWriter(s.getOutputStream()));
        }catch(IOException e){
            System.out.println("Something Bad Happened " + e);
        }
    }


    boolean sendMessage(String msg){

        try{
            NewServer server = new NewServer();
            server.sendtoAll(msg);
            out.println(msg);
            out.flush();   
             System.out.println(server.arrlist.size());
            return true;


        }catch (Exception e) {
            System.out.println("S: Something bad happened :(");
            e.printStackTrace();
            return false;
        }
    }
    String getMessage(){
        try{          

            reps = in.readLine();


        }catch (Exception e) {
            System.out.println("S: Something bad happened :(");
            e.printStackTrace();
        }


            return reps;
     } 
}

Here's the NewServer

public class NewServer{
static ArrayList<MyConnection> arrlist = new ArrayList<MyConnection>();
static boolean push;
static Socket s;

public void sendtoAll(String message){

    for(int i= arrlist.size(); i >= 0; i--){
        MyConnection t3 = arrlist.get(i);
        t3.sendMessage(message);
        if(!t3.sendMessage(message)){
            arrlist.remove(i);
            System.out.println("Client disconnected");
        }
    }

}
public static void main(String args[]){
    try{
        System.out.println("S: Starting server...");
        ServerSocket ssocket = new ServerSocket(8888);
        System.out.println("S: Waiting for connections...");

        while(true){

            s = ssocket.accept();
            System.out.println("SOMEONE CONNECTEDDDDD" + arrlist.size());
            MyConnection t = new MyConnection(s,arrlist);
            arrlist.add(t); //put my connection to arrlist
            t.start();

        }

    }catch(Exception e) {
        System.out.println("Soooomething Bad Happened " + e);
    }
}

Maybe I am missing something - but I couldnt find any place in your code where you actually put objects into your arraylist. Just creating an empty arraylist will not magically put objects into it. **Side note**: the way you iterate your arrlist in `sendtoAll` is bad practice. Just use `for (MyConnection con : arrlist) {` This "downcouting" approach adds a lot of potential confusion to human readers; for a (very very small) gain in performance. Simply dont do it. — GhostCat, Apr 02 '15 at 07:35
MyConnection t = new MyConnection(s,arrlist); arrlist.add(t); — user3339866, Apr 02 '15 at 07:37
@EddyG a for each loop will cause [this error](http://stackoverflow.com/questions/3184883/concurrentmodificationexception-for-arraylist) when it will remove something from the list. So it´s most likely not the best practice to do it — SomeJavaGuy, Apr 02 '15 at 11:03

score 0 · Answer 1 · answered Apr 02 '15 at 11:52

You will not be able to edit the list you are iterating, you could do something like:

public void sendtoAll(String message){
    ArrayList<MyConnection> tempArrlist = new ArrayList<MyConnection>()
    for(int i= arrlist.size(); i >= 0; i--){
        MyConnection t3 = arrlist.get(i);
        t3.sendMessage(message);
        if(t3.sendMessage(message)){
            tempArrlist.add(arrlist.get(i));
        } else {
             System.out.println("Client disconnected");
        }
    }
    arrlist = tempArrlist;
}

How to copy elements of array list from another class to another class

1 Answers1