I am trying to make a program that updates currentTime every second so that in the console it will go 1s, 2s, 3s, 4s and so on.

public static void main(String[] args) throws InterruptedException{
    OSpanel runner = new OSpanel();
    runner.currentTime();
}

public static void currentTime() throws InterruptedException{
    if(true) {
        Date currentTime = new Date();
        while(true) {
            Thread.sleep(1000);
            System.out.println(currentTime);
            Thread.sleep(1000);
            System.out.println(currentTime);
        }
    }
}

CodePudding user response：

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class SOAnswer {
    public static void main(String[] args) {
        ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1);
        long start = System.currentTimeMillis();
        executorService.scheduleAtFixedRate(() -> System.out.println(String.format("%ds", (System.currentTimeMillis() - start) / 1000)), 0, 1, TimeUnit.SECONDS);
    }
}

CodePudding user response：

You are updating currentTime outside of the while loop - you are outputting the date to the console every second but you are not updating the time.

Try this:

Main.java

public static void main(String[] args) throws InterruptedException{
    OSpanel runner = new OSpanel();
    runner.currentTime();
}

OSpanel.java

public void currentTime() throws InterruptedException{
        int counter = 1;
        while (true) {
            System.out.println(counter   "s");
            Thread.sleep(1000);
            counter  ;
        }
    }
}

CodePudding user response：

java.time

The java.util Date-Time API is outdated and error-prone. It is recommended to stop using it completely and switch to the modern Date-Time API^*.

You can use Instant#now to get the current instant of time. In order to get it every second, you can use ScheduledExecutorService#scheduleWithFixedDelay e.g.

import java.time.Instant;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class Main {
    public static void main(String[] args) {
        Executors.newScheduledThreadPool(1)
            .scheduleWithFixedDelay(
                () -> System.out.println(Instant.now()), 
                0, 
                1,
                TimeUnit.SECONDS
            );
    }
}

Output from a sample run:

2021-10-03T13:53:42.462768Z
2021-10-03T13:53:43.469758Z
2021-10-03T13:53:44.470316Z
...

ONLINE DEMO

An Instant represents an instantaneous point on the timeline, normally represented in UTC time. The Z in the output is the timezone designator for a zero-timezone offset. It stands for Zulu and specifies the Etc/UTC timezone (which has the timezone offset of 00:00 hours).

Note: If you want to print just the running second, replace the print statement with the following:

System.out.println(ZonedDateTime.now(ZoneOffset.UTC).getSecond()   "s")

Learn more about the modern Date-Time API from Trail: Date Time.

^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8 APIs available through desugaring and How to use ThreeTenABP in Android Project. Android 8.0 Oreo already provides support for java.time.}

CodePudding user response：

Remove the thread.sleep

while(true) {
         
       System.out.println(currentTime);
      
        }