How do I make a delay in Java?

Question

I am trying to do something in Java and I need something to wait / delay for an amount of seconds in a while loop.

while (true) {     if (i == 3) {         i = 0;     }      ceva[i].setSelected(true);      // I need to wait here      ceva[i].setSelected(false);      // I need to wait here      i++; } 

I want to build a step sequencer and I'm new to Java. Any suggestions?

Answer 1

If you want to pause then use java.util.concurrent.TimeUnit:

TimeUnit.SECONDS.sleep(1); 

To sleep for one second or

TimeUnit.MINUTES.sleep(1); 

To sleep for a minute.

As this is a loop, this presents an inherent problem - drift. Every time you run code and then sleep you will be drifting a little bit from running, say, every second. If this is an issue then don't use sleep.

Further, sleep isn't very flexible when it comes to control.

For running a task every second or at a one second delay I would strongly recommend a ScheduledExecutorService and either scheduleAtFixedRate or scheduleWithFixedDelay.

For example, to run the method myTask every second (Java 8):

public static void main(String[] args) {     final ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();     executorService.scheduleAtFixedRate(App::myTask, 0, 1, TimeUnit.SECONDS); }  private static void myTask() {     System.out.println("Running"); } 

And in Java 7:

public static void main(String[] args) {     final ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();     executorService.scheduleAtFixedRate(new Runnable() {         @Override         public void run() {             myTask();         }     }, 0, 1, TimeUnit.SECONDS); }  private static void myTask() {     System.out.println("Running"); }