Question

I want to call the add function of an HashSet with some delay, but without blocking the current thread. Is there an easy solution to achieve something like this:

Utils.sleep(1000, myHashSet.add(foo)); //added after 1 second
//code here runs immediately without delay
...

Answer 1

You can use ScheduledThreadPoolExecutor.schedule:

ScheduledThreadPoolExecutor exec = new ScheduledThreadPoolExecutor(1);

exec.schedule(new Runnable() {
          public void run() {
              myHashSet.add(foo);
          }
     }, 1, TimeUnit.SECONDS);

It will execute your code after 1 second on a separate thread. Be careful about concurrent modifications of myHashSet though. If you are modifying the collection at the same time from a different thread or trying to iterate over it you may be in trouble and will need to use locks.