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Problem with Java sockets (in tic tac toe game)

I built a tic tac toe two-player game in Java using sockets (no threads). I have a job, except that clients end when the game is finished. Basically, I configured it so that as soon as the game is over (the server recognizes a win or a draw), the server will send a message to two clients. If clients read this particular message, they will “break out” of their do-while loops and close socket connections.

The problem is that whenever one client closes, the other “crashes” - it completes, but does not succeed (it gives an error message). Think of three terminals open — two clients and one server. If I remove "Ctrl-C" (exit) on one client terminal, the other client will stop. Customers should be completely divided, I do not understand why this is happening.

I am going to publish my server code and my client code (after removing the Tic Tac Toe logic) - can anyone see what I'm doing wrong? Thanks!

UPDATE: I added print statements to try-catch, however this does not stop the problem. The error I am getting is this:

Exception in thread "main" java.lang.ClassCastException: java.lang.String at Requester.run(Requester.java:32) at Requester.main(Requester.java:142)

I modified the code below to include all the Tic Tac Toe logic.

  currentPlayer = (Integer) in.readObject();

... right after the first do-try statement. Can anyone see what is happening?

Server

  import java.io.*; import java.net.*; public class Provider { TBoard board = new TBoard(); ServerSocket providerSocket; Socket connection1 = null, connection2 = null; ObjectOutputStream out, out2; ObjectInputStream in, in2; String message; Boolean done = false; int row; int col; Provider() { } void run() { try { providerSocket = new ServerSocket(20092); System.out.println("Waiting for connection..."); connection1 = providerSocket.accept(); System.out.println("Connection received from Player 1 " + connection1.getInetAddress().getHostName()); connection2 = providerSocket.accept(); System.out.println("Connection received from Player 2 " + connection2.getInetAddress().getHostName()); out = new ObjectOutputStream(connection1.getOutputStream()); out2 = new ObjectOutputStream(connection2.getOutputStream()); in = new ObjectInputStream(connection1.getInputStream()); in2 = new ObjectInputStream(connection2.getInputStream()); do { if (board.get_player() == 1) { out.writeObject(board.get_player()); out.flush(); out.writeObject(board.print_board()); out.flush(); } else { out2.writeObject(board.get_player()); out2.flush(); out2.writeObject(board.print_board()); out2.flush(); } sendMessage(board.get_player(), "Please enter a row, press Enter, then enter a column: "); if (board.get_player() == 1) { int[][] c_array = (int[][]) in.readObject(); board.set_array(c_array); } else { int[][] c_array = (int[][]) in2.readObject(); board.set_array(c_array); } if (board.get_player() == 1) { board.set_player(2); } else { board.set_player(1); } if (board.winner() != 0) { System.out.print("The winner is..."); if (board.get_player() == 1) { System.out.println("Player 2!"); } else { System.out.println("Player 1!"); } out.writeObject("bye"); out.flush(); out2.writeObject("bye"); out2.flush(); done = true; } else { if(board.get_player() == 2){ out.writeObject("nothing"); out.flush(); } else{ out2.writeObject("nothing"); out2.flush(); } } } while (done != true); } catch (IOException ioException) { ioException.printStackTrace(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } finally { try { in.close(); out.close(); in2.close(); out2.close(); providerSocket.close(); } catch (IOException ioException) { ioException.printStackTrace(); } } } void sendMessage(int player, String msg) { try { if (player == 1) { out.writeObject(msg); out.flush(); } else { out2.writeObject(msg); out2.flush(); } } catch (IOException ioException) { ioException.printStackTrace(); } } public static void main(String args[]) { Provider server = new Provider(); while (true) { server.run(); } }

}

Customer:

  import java.io.*; import java.net.*; import java.util.Scanner; public class Requester { TBoard board = new TBoard(); Socket requestSocket; ObjectOutputStream out; ObjectInputStream in; String message; String endmessage = ""; int row, col, currentPlayer; Scanner scan = new Scanner(System.in); Requester() { } void run() { try { requestSocket = new Socket("server2.xx.xxxx.xxx", 20092); System.out.println("Connected to localhost in port 20092"); out = new ObjectOutputStream(requestSocket.getOutputStream()); in = new ObjectInputStream(requestSocket.getInputStream()); do { try { currentPlayer = (Integer) in.readObject(); board.set_player(currentPlayer); int[][] b_array = (int[][]) in.readObject(); board.set_array(b_array); for (int i = 0; i < 3; i++) { System.out.println(""); for (int j = 0; j < 3; j++) { if (b_array[i][j] == 1) { System.out.print(" X"); } else if (b_array[i][j] == 2) { System.out.print(" O"); } else { System.out.print(" -"); } } } System.out.println(); message = (String) in.readObject(); System.out.print(message); row = scan.nextInt(); while (row < 0 || row > 2) { System.out .print("Row is invalid, please choose again (0-2): "); row = scan.nextInt(); } col = scan.nextInt(); while (col < 0 || col > 2) { System.out .print("Column is invalid, please choose again (0-2): "); col = scan.nextInt(); } while (!board.make_move(row, col)) { System.out .print("The move is not valid. Please choose another row (0-2): "); row = scan.nextInt(); while (row < 0 || row > 2) { System.out .print("Row is invalid, please choose again (0-2): "); row = scan.nextInt(); } System.out.print("Please choose a column (0-2): "); col = scan.nextInt(); while (col < 0 || col > 2) { System.out .print("Column is invalid, please choose again (0-2): "); row = scan.nextInt(); } } for (int i = 0; i < 3; i++) { System.out.println(""); for (int j = 0; j < 3; j++) { if (b_array[i][j] == 1) { System.out.print(" X"); } else if (b_array[i][j] == 2) { System.out.print(" O"); } else { System.out.print(" -"); } } } System.out.println(); out.writeObject(board.print_board()); out.flush(); endmessage = (String) in.readObject(); } catch (ClassNotFoundException classNot) { System.err.println("data received in unknown format"); } } while (!endmessage.equals("bye")); } catch (UnknownHostException unknownHost) { System.err.println("You are trying to connect to an unknown host!"); } catch (IOException ioException) { ioException.printStackTrace(); } finally { try { in.close(); out.close(); requestSocket.close(); } catch (IOException ioException) { ioException.printStackTrace(); } } } void sendMessage(int msg) { try { out.writeObject(msg); out.flush(); } catch (IOException ioException) { ioException.printStackTrace(); } } public static void main(String args[]) { Requester client = new Requester(); client.run(); }

}

... Any help would be wonderful, I stuck to it one day. Thanks!

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4 answers

When one of the two users closes the program. The connection is breaking. Then, the socket class throws an IOException, which you catch:

  ... } catch (IOException ioException) { ioException.printStackTrace(); } ...

But, having caught this, you are not doing anything. You should add some messages and say that the connection is broken. I think your program does not crash, it just stops because it catches the exit and closes the threads in finnaly .

Hope this helps.

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In your Server class in your catch (IOException ioException) {}

you can catch which ObjectInputStream object threw an exception (because the client-client closes the IOException on the server side) and then sends the other client a “win because your opponent disconnected”

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I think your “sync” is stuck. Try printing the variables you are reading. And also print what you think you will read.

Exemple:

 // Set Current Player System.out.println("Reading current player"); Object inputCP = in.readObject(); System.out.println(inputCP.getClass().getName() + " " + inputCP); board.set_player((int) (Integer) inputCP);

Do the same for recording and compare the outputs. Thus, you can see what is wrong with the synchronization of sending and receiving data.

Note. If you write an ObjectOutputStream, it automatically discards.

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Kill in the dark here, but catching an IOException will not solve the ClassCastException exception problem, which is the error you say:

 Exception in thread "main" java.lang.ClassCastException: java.lang.String at Requester.run(Requester.java:32) at Requester.main(Requester.java:142)

And you say line 32 of Requester:

 currentPlayer = (Integer) in.readObject();

You are trying to insert in.readObject () into an Integer, but it is actually a String, hence this is an exception.

But don't just catch the exception, practice why you get a string instead of an integer.

My guess is the server code you posted and the void sendMessage (int player, String msg) method. It looks like you are sending a String message, but expect an integer on the other end. you can clean it up a bit

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