java 计算程序执行时间

public class systemdemo {
    public static void main(String[] args) {
        long startTime=System.currentTimeMillis();
        int sum=0;
        for(int i=0;i<999999999;i++){
            sum+=i;
        }
        long endTime=System.currentTimeMillis();
        System.out.println("Time cost:"+(endTime-startTime)+"millis");
    }
}