实现一个很简单的计时器类

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class StopWatch {
private final static Logger LOG = LoggerFactory.getLogger(StopWatch.class);
//  程序开始运行的时间
private final long start;

public StopWatch() {
start = System.currentTimeMillis();
}

public double elapsedTime() {
long now = System.currentTimeMillis();
return (now - start) / 1000.0;
}

public void logElapsedTime(){
LOG.info("used time "+elapsedTime()+"s");
}
}