Issues with networking in my Java game, Client crashes when I try and read from the server input

Question

A buddy and I have been programming a code game over the last 2 weeks, it is intended to be a multiplayer game with the ability to have 2 players play against each other.

I am running into an issue when I try and implement the server-client relationship. My client crashes when it tries to receive information from the server.

The main issue is in the GameplayState.java file. the getTile() method makes the client crash, so I am assuming the issue lies with how I'm handling the information being sent from the server.

Is there a way to fix this and prevent the crashing? would there be a better way to achieve what I am trying to do?

We are using the lwjgl, Slick2d libs

Specifically its the call: serverIn.readLine(); that makes crap go crazy.

Finally receive an error

Wed Jun 13 21:03:58 ADT 2012 ERROR:For input string: ",B6,W5,B2,W7,B,B,W,W" java.lang.NumberFormatException: For input string: ",B6,W5,B2,W7,B,B,W,W" at java.lang.NumberFormatException.forInputString(Unknown Source) at java.lang.Integer.parseInt(Unknown Source) at java.lang.Integer.parseInt(Unknown Source) at GameplayState.getTile(GameplayState.java:168) at GameplayState.update(GameplayState.java:124) at org.newdawn.slick.state.StateBasedGame.update(StateBasedGame.java:268) at org.newdawn.slick.GameContainer.updateAndRender(GameContainer.java:657) at org.newdawn.slick.AppGameContainer.gameLoop(AppGameContainer.java:408) at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:318) at CodaClient.main(CodaClient.java:34) Wed Jun 13 21:03:58 ADT 2012 ERROR:Game.update() failure - check the game code. org.newdawn.slick.SlickException: Game.update() failure - check the game code. at org.newdawn.slick.GameContainer.updateAndRender(GameContainer.java:663) at org.newdawn.slick.AppGameContainer.gameLoop(AppGameContainer.java:408) at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:318) at CodaClient.main(CodaClient.java:34)

Relevant server source code below:

Because I'm getting flak for putting all the code in, for ease, I will bold the statements that say what files the issue arises in

Client Code

• GameState
• OptionsState
• CodaClient(main)
• MainMenuState

Server Code

• Server(main)
• GameManager
• ClientThread

Answer 1

Error stacks go from the most recent call to the least recent, so the most recent line is what happened, and all the rest are what it happened within, what method that was called from, what method that was called from, and so on.

Wed Jun 13 21:03:58 ADT 2012 ERROR:For input string: ",B6,W5,B2,W7,B,B,W,W"
java.lang.NumberFormatException: For input string: ",B6,W5,B2,W7,B,B,W,W"
    at java.lang.NumberFormatException.forInputString(Unknown Source)
    at java.lang.Integer.parseInt(Unknown Source)
    at java.lang.Integer.parseInt(Unknown Source)
    at GameplayState.getTile(GameplayState.java:168)
    at GameplayState.update(GameplayState.java:124)

Or to break it down...

// this is the exception time & message
Wed Jun 13 21:03:58 ADT 2012 ERROR:For input string: ",B6,W5,B2,W7,B,B,W,W"
// this is the exception itself. It's a NumberFormatException, meaning the number
// was of an invalid format. Which is obvious, since the string here isn't a number.
java.lang.NumberFormatException: For input string: ",B6,W5,B2,W7,B,B,W,W"
// the NumberFormatException was created within this method (obviously a helper for
// creating NumberFormatExceptions)
    at java.lang.NumberFormatException.forInputString(Unknown Source)
// this method ^ was called by the following method, which was given an invalid input
    at java.lang.Integer.parseInt(Unknown Source)
// ... which was in turn called by this one ...
    at java.lang.Integer.parseInt(Unknown Source)
// the above parseInt was called within YOUR getTile method, leading to the exception
    at GameplayState.getTile(GameplayState.java:168)
// which was called within your normal game update.
    at GameplayState.update(GameplayState.java:124)
// and so on.

You called parseInt with an invalid input it obviously can't turn into a number (because it isn't a number), so of course it's going to throw an exception saying it can't do that - that's exactly what's supposed to happen.

Let's see what you're doing in getTile() which is the method that parseInt is called within.

private void getTile() {

    //System.out.println(serverResponse);
    if(serverResponse != "")
        currentTile = new Tile(Integer.parseInt(serverResponse.substring(1)), serverResponse.charAt(0));
}

String.substring(1) returns the string from position 1 (i.e. after the first character) to its end, which in this case ends up as something like ,B6,W5,B2,W7,B,B,W,W. Here's how you stop getting your error: don't do that.

If you meant to just take the first digit, use:

• serverResponse.substring(0, 1), or
• serverResponse.charAt(0), or
• serverResponse[0] (this would be the neatest way to do that in Java, if it's allowed).

If you meant to do something else, well, it's doing this currently. Code it to do something else instead. You have a logic error which means it's up to you to figure out how to get it to do what you want it to do.

Your lesson:

• Read the stack trace
• Debug your code
• Remember your logic could be the problem (it is not perfect)