刚学java，字符串生成器和循环的有关问题

public static void main(String args[]){        String s="aaaaaa";        StringBuilder aa=new StringBuilder(s);        //long startTime=System.currentTimeMillis();        for(long i=0;i<1000;i++){            aa.append(i);        }        //long lengTime=System.currentTimeMillis();        //long time=lengTime-startTime;        System.out.println(aa);        //System.out.println(time);                        }