>[success] # 知识点 * 类型转换 String 和 StringBuilder ~~~ public class TestStr { public static void main(String[] args) { StringBuilder sb1 = new StringBuilder("hello"); // 转换为string 类型 String str = sb1.toString(); // 转换为StringBuilder StringBuilder sb2 = new StringBuilder(str); } } ~~~ * 执行效率 1. String、StringBuilder、StringBuffer之间效率谁高？排列如何？`String < StringBuffer < StringBuilder`