You didn't give me enough code  to tell if this is will fix it but
here it goes:

If you are extending Frame, then go to the method where you are
checking for the Window close, when it closes, just disconnect. If
you're extending JFrame, you'll have to overwrite their method.
Sorry I would elaborate but the bell rings in 2 minutes and then I
have US History.

Ok... That code  is the server... the client(of which there can be as
many as you like...thousands) is running a different program...
I wan't to find out if the client is still connected on the other end.
Thats what this part of the code is all about:

/*30*/ if(/*find out if client has disconnected*/)
/*31*/ {
/*32*/ removeConnection(i);
/*33*/ }

is there some kind of method in java.net.Socket that can figure out if
the client has disconnected?
I've tried quite a few methods, but none of them seem to work.

I don't know if this will help, but here is what I did last year in my
second year networking subject.

Essentially to catch you up to what is happening is that the server  has
threaded this process. When it receives a IOException because someone
had left the server it Excepts and then runs the finally part of the
try/catch/finally.

I don't know how prop


public void run() {

String thisLine;
try {
thisLine = br.readLine();

user = thisLine;
client.setUsername(user);
joinSend(this.user);
thisLine = br.readLine();
while (thisLine != null) {
broadcast(this.user, thisLine);

thisLine = br.readLine();
}
} catch (IOException e) {
if (debug) System.err.println("Removing
this user + :"+this.user);
} finally {
synchronized (clients) {
clients.remove(this);
partSend(this.user);
}
}
}

create antother thread 4 each client conneciton, whenever a connection is idle
for a
predefined time(1min) this thread will send an AYT(are you there?) message. so
if
your soket has broken down, you cannot send ayt pdu from soket and this means
your client connection closed with an undefined and un controlled way.if u use
different
kinds of programming env. in your client-server model (like vbasic clients,java
servers...)
u always encounter problems like this.

so the most generic, reliable and the traditional way to check a soket
connection is AYT
messages.