Netbeans warns you about sleep() and not about join() in Java Threading

if i put a thread to sleep in a loop, netbeans gives me a caution saying Invoking Thread.sleep in loop can cause performance problems. However, if i were to replace the sleep with join, no such caution is given. Both versions compile and work fine tho. My code is below (check the last few lines for "Thread.sleep() vs t.join()").

public class Test{

//Display a message, preceded by the name of the current thread
static void threadMessage(String message) {
String threadName = Thread.currentThread().getName();
System.out.format("%s: %s%n", threadName, message);
}

private static class MessageLoop implements Runnable {
public void run() {
String importantInfo[] = {
"Mares eat oats",
"Does eat oats",
"Little lambs eat ivy",
"A kid will eat ivy too"
};
try {
for (int i = 0; i < importantInfo.length; i++) { //Pause for 4 seconds Thread.sleep(4000); //Print a message threadMessage(importantInfo[i]); } } catch (InterruptedException e) { threadMessage("I wasn't done!"); } } } public static void main(String args[]) throws InterruptedException { //Delay, in milliseconds before we interrupt MessageLoop //thread (default one hour). long patience = 1000 * 60 * 60; //If command line argument present, gives patience in seconds. if (args.length > 0) {
try {
patience = Long.parseLong(args[0]) * 1000;
} catch (NumberFormatException e) {
System.err.println("Argument must be an integer.");
System.exit(1);
}

}

threadMessage("Starting MessageLoop thread");
long startTime = System.currentTimeMillis();
Thread t = new Thread(new MessageLoop());
t.start();

threadMessage("Waiting for MessageLoop thread to finish");
//loop until MessageLoop thread exits
while (t.isAlive()) {
threadMessage("Still waiting...");
//Wait maximum of 1 second for MessageLoop thread to
//finish.
/*******LOOK HERE**********************/
Thread.sleep(1000);//issues caution unlike t.join(1000)
/**************************************/
if (((System.currentTimeMillis() - startTime) > patience) &&
t.isAlive()) {
threadMessage("Tired of waiting!");
t.interrupt();
//Shouldn't be long now -- wait indefinitely
t.join();
}

}
threadMessage("Finally!");
}
}

Why does netbeans throw the caution?
Its Because::
There is a difference between join() and sleep(). join() will wait until the timeout expires or the thread finishes. sleep() will just wait for the specified amount of time unless interrupted. So it is perfectly possible for join() to return much faster than the specified time.

The reason why Netbeans warns you about sleep() and not about join() is precisely that difference. join() waits for something meaningful while sleep() just sits there doing nothing. If you aren't waiting for something, then why would you want to wait at all? It is rarely meaningful, hence the warning.