How do I make a delay in Java?

问题:

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?

回答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\");
}

回答2:

Use Thread.sleep(1000);

1000 is the number of milliseconds that the program will pause.

try
{
    Thread.sleep(1000);
}
catch(InterruptedException ex)
{
    Thread.currentThread().interrupt();
}

回答3:

You need to use the Thread.sleep() call.

More info here: http://docs.oracle.com/javase/tutorial/essential/concurrency/sleep.html

回答4:

Using TimeUnit.SECONDS.sleep(1); or Thread.sleep(1000); Is acceptable way to do it. In both cases you have to catch InterruptedExceptionwhich makes your code Bulky.There is an Open Source java library called MgntUtils (written by me) that provides utility that already deals with InterruptedException inside. So your code would just include one line:

TimeUtils.sleepFor(1, TimeUnit.SECONDS);

See the javadoc here. You can access library from Maven Central or from Github. The article explaining about the library could be found here

回答5:

use Thread.sleep(100); The unit of time is milliseconds

for an example

public class SleepMessages {
    public static void main(String args[])
        throws InterruptedException {
        String importantInfo[] = {
            \"Mares eat oats\",
            \"Does eat oats\",
            \"Little lambs eat ivy\",
            \"A kid will eat ivy too\"
        };

        for (int i = 0;
             i < importantInfo.length;
             i++) {
            //Pause for 4 seconds
            Thread.sleep(4000);
            //Print a message
            System.out.println(importantInfo[i]);
        }
    }
}