Question

I have a process which should react on some events. So when playFromList() is called it plays some sound from soundpool. Then in a thread I set a flag and for 3,5 seconds it should not play any sounds.

What I got is: It plays sound and if than wait 3,5 seconds. If playFromList() is called 5 times in 3,5 seconds it still gets to SoundManager.playSound(listNr), and still is done in 17,5 seconds. And its not exactly what I wanted. I wanted method SoundManager.playSound(listNr) called only once.

public class Settings{
    public static boolean flag = false;
}

 public class Main{
 public void playFromList(int listNr,int g){

        if(!Settings.flag){
            SoundManager.playSound(listNr);
            if(g ==0){
                mpVolume((float) 0.3);
                t5sec.run();
            }else{pauseMus();}      
        }           
    }

        private Handler vijfSeconden = new Handler(){
            public void handleMessage(Message msg){
                mpVolume((float)0.8);
            }
        };
        Thread t5sec = new Thread(){
            public void run(){
                if(Settings.flag == false){
                    Settings.flag = true;
                    try {
                        Thread.sleep(3500); 
                    } catch (InterruptedException e) {
                        Settings.flag = false;
                        e.printStackTrace();
                    }
                    vijfSeconden.sendEmptyMessage(0);

                    Settings.flag = false;
                }
            }
        };
 }

Answer 1

There are few problems with the code. Probably most important thing that is strange is
t5sec.run(), in Java you you should use start method on the Thread object to start new Thread. As written it will execute in the calling thread.
Second problem is absolute lack of synchronization, one way to fix that, I guess, would be to use AtomicBoolean instead of boolean in Settings.flag

Another issue is that it is quite expensive to start new thread every time. It is a bit hard to tell from the description precisely what you want to do, but if my understanding is correct you should just do something like this:

if ( (System.currentTimeInMillis() - lastTimePlayed) < 3500) {
 playSound();
 lastTimePlayed = System.currentTimeInMillis();
}

that’s it and no threads required. You might want to use AtomicInteger to hold lastTimePlayed value if you want your class to be thread safe.