String类为什么要用final修饰?
final修饰符的意义?
https://www.cnblogs.com/loren-Yang/p/13380318.html
String类被实现的目标是什么?
效率和安全
如何实现期望?
参考文献
https://www.jianshu.com/p/9c7f5daac283
https://www.zhihu.com/question/31345592
https://blog.csdn.net/qq_27093465/article/details/52190915