java语言基础--获取毫秒及字符串拼接的性能问题

public class Main4 {

    public static void main(String[] args) {
        //获取毫秒数
        long now = System.currentTimeMillis();
        System.out.println(now);
        
        //演示String和StringBuffer拼接1000次所用的时间
        String s1 = "";
        StringBuffer s2 = new  StringBuffer(1000);
        //String
        long before = System.currentTimeMillis();
        for (int i = 0 ; i <100000; i ++) {
            s1 += 1;
        }
        long after = System.currentTimeMillis();
        System.out.println(after - before);
        //StringBuffer
        long bbefore = System.currentTimeMillis();
        for (int i = 0 ; i <100000; i ++) {
            s2.append(i);
        }
        long bafter = System.currentTimeMillis();
        System.out.println(bafter - bbefore);
    }
}