1．理解String与StringBuffer的区别，掌握String对象的常用创建方式

2.理解String常量采用对象池保存的方式

3.熟练掌握String的各种常用方法

4.掌握StringBuffer在做字符串连接时的优势

-1. Understanding the difference between String and StringBuffer, String object used to create master mode 2. Understand the String object pool kept constant by the way 3. String master a variety of commonly used method 4. Master StringBuffer connection string in the advantages of doing