区别：
https://www.cnblogs.com/su-feng/p/6659064.html
https://blog.csdn.net/liangjunhua5/article/details/70156963
stringbuffer
https://www.cnblogs.com/liu-chao-feng/p/5636063.html
stringbuilder
和上面类似
StringBuilder和StringBuffer
原文：https://www.cnblogs.com/vhyc/p/9221176.html
