The difference between scheduleWithFixedDelay and scheduleAtFixedRate

scheduleWithFixedDelay使用

public class MainDemo {
    
public static int times = 0;
    public static void main(String[] args) {
    

        ScheduledThreadPoolExecutor scheduledThreadPoolExecutor   = new ScheduledThreadPoolExecutor(1);
       
        scheduledThreadPoolExecutor.scheduleWithFixedDelay(new Runnable() {
    
            @Override
            public void run() {
    
                try {
    
                    System.out.println( "开始执行时间" + System.currentTimeMillis());
                    Thread.sleep(4000);
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
                System.out.println( "执行结束时间" + System.currentTimeMillis());
            }
        },0,3, TimeUnit.SECONDS);
    }
}

开始执行时间1658308204447
执行结束时间1658308208448
开始执行时间1658308211450
执行结束时间1658308215456
开始执行时间1658308218458
执行结束时间1658308222459
开始执行时间1658308225461
执行结束时间1658308229462
开始执行时间1658308232462
执行结束时间1658308236463
开始执行时间1658308239463
执行结束时间1658308243466
开始执行时间1658308246467
执行结束时间1658308250467
开始执行时间1658308253470

scheduleAtFixedRate的使用

import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;


public class MainDemo {
    
public static int times = 0;
    public static void main(String[] args) {
    

        ScheduledThreadPoolExecutor scheduledThreadPoolExecutor   = new ScheduledThreadPoolExecutor(1);
        scheduledThreadPoolExecutor.scheduleAtFixedRate(new Runnable() {
    
            @Override
            public void run() {
    
                try {
    
                    System.out.println( "开始执行时间" + System.currentTimeMillis());
                    Thread.sleep(4000);
                } catch (InterruptedException e) {
    
                    e.printStackTrace();
                }
                System.out.println( "执行结束时间" + System.currentTimeMillis());
            }
        },0,3, TimeUnit.SECONDS);
        
    }

}

总结

scheduleAtFixedRateA function is after the program in the function body has finished executing,立即执行.

而scheduleWithFixedDelayAfter the program execution of the function body is completed,再delayExecute after set time.