java - Server Application: Only works with a println output -

apologies ambiguous title - couldn't think how word title.

basically, i'm playing around creating simple server/client programs in java. server runs thread check new connections, if connection found - creates thread , connection object connection.

problem comes in @ thread checks new connections - didn't work, until started error checking , when added in line:

system.out.println(""); 

it started work should. removing line causes no new threads added connections. assumed providing enough delay thread run or something, put in loop while see if worked - nothing else has worked apart 1 simple line.

here's code creating new connection threads:

    class threadcreator implements runnable {      threadcreator() {      }      public void run() {         while(true) {             system.out.println("why work??");             for(int = 0; < connections.size(); i++) {                 if(connections.get(i).thread == false) {                     runnable readrunnable = new read(connections.get(i));                     thread readthread = new thread(readrunnable, "mwhahah");                     readthread.setpriority(thread.max_priority);                     readthread.start();                     connections.get(i).thread = true;                     system.out.println("thread created");                 }             }         }     } } 

i can't imagine going wrong..?

one thing keep in mind system.out.println() involves synchronization and call wait() somewhere (since println() out-flushes , waits response visible (or @ least passed other process) until returning.

this can easily "fix" multi-threaded program if synchronization problem.